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SPE/EAGE European Unconventional Resources Conference and Exhibition
- Conference date: February 25-27, 2014
- Location: Vienna, Austria
- Published: 25 February 2014
1 - 20 of 96 results
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Application of Support Vector Machine to Account for Hydraulic and Natural Fracture Interaction in Unconventional Naturally Fractured Reservoirs
Authors R. Keshavarzi and R. JahanbakhshiHydraulic and natural fracture interaction is always a matter of debate in petroleum geomechanics especially in unconventional reservoirs since without fractures it is not possible to commercially recover hydrocarbon from this type of reservoirs. Hydraulic fracturing in the presence of natural fractures can significantly affect the behavior of the induced fracture propagation through the rock and causes a complex network of fractures. Although hydraulic and natural fracture interaction can lead to natural fracture system activation and productivity increase but without a precise geomechanical and operational analysis it may lead to pre-mature screenout, arrest of the fracture propagation and fracture offsets. In this study, the problem of hydraulic fracture propagation in the presence of natural fracture has been investigated through a Support Vector Machine (SVM) approach. So, a SVM model has been developed to predict hydraulic fracturing path due to interaction with natural fracture followed by a forward selection sensitivity analysis based on accuracy, sensitivity and specificity of the developed SVM to determine the most influential parameters on this complicated phenomenon. Geomechanical and operational effective parameters in hydraulic and natural fracture interaction such as horizontal differential stress, angle of approach, interfacial coefficient of friction, young’s modulus of the rock and flow rate of fracturing fluid are the inputs and hydraulic fracturing path (opening/crossing natural fracture) when it intercepts a natural fracture is the output of the developed SVM model. The results have shown the capabilities of the developed SVM model to predict hydraulic fracturing path as interacting with natural fracture in different conditions of horizontal differential stress, angle of approach, interfacial coefficient of friction, young’s modulus of the rock and flow rate of fracturing fluid. Also, the result of sensitivity analysis based on accuracy of the SVM model has shown that geomechanical parameters which are the angle of approach, horizontal differential stress and interfacial coefficient of friction play the most important roles in hydraulic fracture behavior in the vicinity of natural fracture while flow rate of fracturing fluid and young’s modulus of the rock are in the second priority.
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Research on Fractured Horizontal Wells Productivity and Productivity Influence in Shale Gas Reservoir
Authors Weiyang Xie and Xiaoping LiAbstractBased on large number of shale gas exploration and development literature research, this paper describe the characteristics, accumulation regularity, adsorption and desorption properties of shale gas which are different from conventional gas reservoir. Langmuir isotherm law and Fick diffusion law are used to established the desorption gas steady diffusion rate expression. Three research works have been done, first, established the production formula of fractured horizontal well based on the model of Genliang Guo rectangle fractured horizontal flow, fracture angle and desorption gas steady diffusion rate are employed to improve the production formula. Second, interact of fractures and desorption are considered, equivalent filtrational resistance is used to establish a capsule model of shale gas steady flow, a new production formula of fractured horizontal well in shale gas reservoir has been derived by the new flow model. At last, rationality of the two formulas has been proved by the calculation of programing based on the field data. Analysised the production influence of formation parameter, horizontal well drilling factors, fracturing effect and desorption gas steady diffusion rate.The production formula of fractured horizontal well in shale gas reservoir and the research of production influence can be used in productivity prediction of later period shale gas reservoir fractured horizontal development. It can also interpret the parameters selection of drilling and hydrofracture more accurately for shale gas reservoir. Optimization design of shale gas reservoir development mode can be improved by the production formula and effect factors research. Desorption gas steady diffusion rate computational method provided us with deeper research about years of stable production, proration, reasonable production system in shale gas reservoir development and how desorption affect production of fractured horizontal shale gas wells.
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A New Geomechanical Model Explaining Source Mechanisms of Events Induced by Hydraulic Fracturing in Shale
Authors Leo Eisner and Frantisek StanekAbstractOptimization of stimulation is key to successful development of unconventional reservoirs. Microseismic monitoring is the most powerful tool to help us understand where and what is happening during and after the stimulation. Yet very little is understood about the relationship between microseismicity and hydraulic fractures: some believe microseismic events are part of the hydraulic fractures, some believe they are resulting from stress changes and fluid leak-off. Microseismic datasets with accurate event locations complemented with source mechanisms lead us to a new level of understanding of the interaction between hydraulic fracturing and seismic response. There are at least four geomechanical models to explain observed failure mechanisms and the opening (or closing) of hydraulic fractures (seismic tensile opening, leak-off cloud of seismicity around the hydraulic fracture, shearing between aseismic tensile opening and horizontal fractures shearing on vertical planes). Unfortunately none of these models is consistent with observations presented in this study. Hence we developed a new geomechanical model of bedding plane slippage and vertical shearing induced by hydraulic fractures in shale reservoirs.
We present a case study including detailed source mechanism inversion for a microseismic dataset from hydraulic fracturing of a shale gas play in the North America. We observe source mechanisms dominated by shear failure with dip-slip and strike-slip sense of motion. The dip-slip mechanisms are prevailingly oriented with shear planes along the maximum horizontal stress. This can be explained as slippage on beddings planes caused by aseismic opening of hydraulic fractures. The strike-slip mechanism show small but real components of non-shear deformation. This can be also explained as slippage on vertical plane perpendicular to maximum horizontal stress with slight opening as these events are direct part of the hydraulic fracture. This model explains large energy difference between seismic and hydraulic energy, and prevailing orientation of the shear planes of the induced microseismic events. In addition, the bedding planes are weak planes in the shale formation likely to fail. The model can better constrain fundamental parameters of induced hydraulic fractures and describe hydraulic fractures and their interaction with the shale plays.
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Stakeholder Concerns Against Shale Gas Developments in Europe - The Relevance of Water Management
Authors Walter Heinz and Dieter HillerAbstractThe exploration of shale gas resources in Europe is moving at a slow pace, despite the fact that drilling for reservoir characterization is essential for any further planning. Whether shale gas development in certain regions is economically feasible at all and what such development activities might entail can’t be determined in the absence of critical data. Yet, there is widespread public resistance that influences political decision making and permitting, and that sometimes doesn’t even allow for exploration. Most of the stakeholders concerns are related to perceived environmental risks for water resources as a result of hydraulic fracturing. The main themes are concerns about the contamination of water bodies by fracturing chemicals, methane or flowback water, or concerns about the depletion of groundwater and surface water.
While some of those perceived risks may be overestimated or unsubstantiated, there are real risks that have to be addressed by thorough assessments of the environmental, health and social impacts, and by an integrated approach to water management from sourcing to final disposal. This includes the transportation and distribution logistics for water and wastewater movements. It is essential to establish relevant reference and baseline data on groundwater and surface water systems well ahead of project implementation, to assess risks in a fashion that is understood by interested stakeholders, to define proactive and reactive resource protection measures, and to monitor performance.
This paper suggests an integrated approach to water management that combines the elements of impact assessments, scientific and technical data gathering, and the monitoring of potential impacts across the life cycle of a shale gas project, as well as sourcing, transportation and disposal strategies. All results and measures taken need to be communicated and documented in a clear and transparent manner.
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CBM Development Scenario Optimization for Production Sharing Contract, Case Study: Sumbagsel Field, Indonesia
Authors Felik Ferdian, Adrinal Ilyas and Vina MediyantiAbstractIndonesia according to research by Resource International Inc. Advance. (ARII) along with the Directorate General of Oil and Gas – Ministry of Energy and Mineral Resources has potential resource 453 TCF of CBM which is divided into 11 (eleven) basin on the island of Sumatra, Borneo, Java and Sulawesi. The results of CBM product is expected to be a solution to Indonesia’s potential energy shortages in the future relying on energy sources from oil and natural gas.
The utilization of CBM in Indonesia following the fiscal term of Production Sharing Contract (PSC) with a validity period of 30 years. CBM reservoir characteristics are different from conventional gas with smaller permeability, predominantly adsorbed gas and under-saturated conditions require draining the water content (dewatering) before the production period that requires careful planning to produce a viable project either in terms of technical, economic and commercial.
Simulations conducted in Sumbagsel Field in Southern Sumatra, Indonesia, seeking development planning optimization by creating drilling scenarios of CBM wells with a certain amount of accumulation to get a good view of the economic indicators of Net Present Value (NPV), Internal Rate of Return (IRR), Profitability Index (PI) and Payback of Time (POT). The results showed that CBM development can not be done with conventional gas development model approach which uses ‘chuck management system’ to control the production, while the properly management is required in the development of CBM drilling where the number of production wells will be proportional to the increase of production. Knowledge of reservoir characteristics and production optimization management of the number of drilling development wells during fiscal term contract with the production sharing contract will result in the economic development of CBM.
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The Impact of Multiphase Flow on Well Testing Models in Gas Hydrate Reservoirs without Crossflow
More LessAbstractGas hydrates will dissociate to gas and water at pressures below the equilibrium pressure or temperatures above the equilibrium temperature. Moreover, some hydrate reservoirs have considerable amounts of mobile gas and water coexisting with the hydrates in the formation. This implies, fluid diffusivity in such reservoirs is predominantly multiphase and hence addressing multiphase flow in such reservoirs becomes very vital.
Conventionally, most well testing models address diffusivity in porous media by assuming a single/dominant flowing phase or addressing the fluid phases separately. If a huge discrepancy exists between the fluid saturations, the fluid with the highest saturation could denote the dominant flowing phase, depending on the fraction flow model, and the correction with the multiphase model becomes trivial, as also seen with most conventional gas reservoirs with low water saturation. However, if the saturations of the different phases do not vastly differ from one another, multiphase well testing models give a more accurate prediction of reservoir behavior. The definition of the multiphase dimensionless time becomes very essential in predicting the diffusivity of the fluids and for well test designs.
The multiphase flow models developed here are based on mass balance and volumetric material balance approaches. The total mobility is derived for both the mass balance and volumetric material balance models, further related to fraction flow models. The total mobility model developed by Perrine, used by most reservoir engineering calculations is not addressed in detail for this work, as this does not fulfill mass conservation considered in this paper. Due to the non-linearity of the diffusivity equation, the multiphase diffusivity model addressed here includes pseudo-pressure and pseudo-time integrals. The solutions to the diffusivity equations for multiphase flow are given for both approaches. The differences between both models and their limitations are addressed and highlighted with illustrative examples.
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Sweetspotting of the First Appraisal Campaign of Unconventional Resource Play in Kuwait
AbstractOrganic rich Kerogen layer of Lower Kimmeridgian to Upper Oxfordian age, deposited throughout Kuwait, is a TOC rich layer with varying TOC content between 2 to 20 wt% (in the vertical section) and having an average TOC of about 8 wt%. The depth of occurrence of this layer favorably places this zone to be having potential in rich gas condensate resource in the northern part of Kuwait. This layer occurs at a depth of 14000–16000 ft with a reservoir temperature of 270°-275°F, pressure of 11000 psi and average thickness of over 50ft. This is one of the main source rocks for majority of the oil and gas fields of Kuwait. This Kerogen section is penetrated through a number of vertical wells, as part of development of deeper reservoirs in this area, which offers an excellent opportunity to evaluate this section through core and open-hole log data. Because of the strong acoustic contrast with the overlying and underlying layers, this reservoir section is a very strong mappable seismic reflector.
As part of appraising the potential of this layer, as a resource play, a comprehensive success criteria has been worked out for location selection. An integration of all available geo-scientific data such as geochemical, 3D seismic attributes, petrophysical analysis, borehole image interpretations, geo-mechanical, core and mud logs has been carried out. The above data integration/analysis was combined with the success criteria, leading to selection of sweet-spots for planning the first dedicated horizontal well targeted on this layer.
This paper presents the success criteria worked out and the integration of data for high grading the locale – sweet-spots, for the first set of horizontal wells for appraising this deep HP-HT unconventional play of Kuwait.
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Drainage Estimation and Proppant Placement Evaluation from Microseismic Data
Authors Carl W. Neuhaus, Mary Ellison, Cherie Telker and Keith BlairAbstractIn this case study we outline how microseismic analysis can be used to optimize treatment design and determine the portion of the stimulated rock volume that should be productive. To begin, microseismic data was acquired with a permanently installed shallow buried array of geophones during the hydraulic fracturing of 17 wells in the Marcellus Shale. The processed results were used to conduct a multi-disciplinary study integrating geology, geomechanics, reservoir and completion engineering, and ultimately, production data. A stress inversion from focal mechanisms was performed, and correlations were made between hydrocarbon production and microseismic results. That work, in conjunction with the variability in the stimulation approach, was used to optimize the treatment design on an individual wellbore and on a field development scale. Treatment design analysis indicated optimum wellbore spacing, stage spacing and length as well as evaluated the vertical coverage of the treatment within the Marcellus. Incorporating information from source mechanisms, an event magnitude calibrated discrete fracture network (DFN) was modeled taking into account the seismic energy of the events, rock properties, the injected fluid volume and efficiency. Evaluating the placement of proppant inside the DFN enables distinction between the part of the stimulated rock volume (SRV) that contributes to production in the long term, and the part of the reservoir that was affected by the treatment but may not be hydraulically connected over a longer period of time. Finally, the permeability of the stimulated fracture system was calculated from the microseismic results. This allows for the evaluation of the drainage volume and estimation of production.
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A Physics-Based Method for Production Data Analysis of Tight and Shale Petroleum Reservoirs Using Succession of Pseudo-Steady States
Authors M.S. Shahamat, L. Mattar and R. AguileraAbstractAnalysis of production data from tight and shale reservoirs requires the use of complex models for which the inputs are rarely known. The same objectives can also be achieved by knowing only the overall (bulk) characteristics of the reservoir, with no need for all the detailed rarely known inputs. In this work, we introduce the concept of continuous succession of pseudo-steady states (SPSS) as a method to perform the analysis of production data. It requires very little input data yet is based on rigorous engineering concepts which works during the transient as well as the boundary dominated flow periods.
This method consists of a combination of three simple and well-known equations: material balance, distance of investigation and boundary dominated flow. It is a form of a capacitance-resistance methodology (CRM) in which the material balance equation over the investigated region represents the capacitance, and the boundary dominated flow equation represents the resistance. The flow regime in the region of investigation (whose areal extent varies with time during transient flow) is assumed to be pseudo-steady state. This region is depleted at a rate controlled by the material balance equation.
The initial flow rate and flowing pressure are used to define the resistance, and the distance of investigation defines the capacitance. The capacitance and resistance are then used in a stepwise procedure to calculate the depletion and the new rates or flowing pressures. The method was tested, for linear flow geometry, against analytical solutions for liquids and numerical simulations for gas reservoirs, exhibiting both transient and boundary dominated flow. Excellent agreement was obtained, thus corroborating the validity of the method developed in this paper.
The proposed method is easy to implement in a spreadsheet application. It indicates that complex systems with complicated mathematical (e.g. Laplace space) solutions can be represented adequately using simple concepts. The approach offers a new insight into production analysis of tight and shale reservoirs, using familiar and easy-to-understand reservoir engineering principles.
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First Openhole Hydraulic Fracturing Treatment Using Diverter Technology in India
Authors Faraaz Adil, Karan Pande and Bhavna RainaAbstractThis paper discusses the hydraulic fracturing (HF) treatment of a tight gas well owned by a major power service company in India. The objective was to perform a HF treatment on the openhole (OH) section to assess the reservoir potential for future development work. The success of this treatment could unlock the oil and gas reserves in this area of the country, which are estimated to be massive.
The fracturing treatment of the tight gas reservoir was to be performed under these conditions for the first time in the area, so there was no previous information to help design the treatment nor predict the result. Injectivity and mini-frac tests were performed to analyze the reservoir properties before designing the final fracturing design and execution.
One of the major challenges was to perform the fracturing treatment on an OH section under extremely strenuous operational deadlines, which eliminated the options of using any more suitable well completion methods. Thus, it was proposed to use a diverting agent in the fracturing treatment design to help maximize the stimulated reservoir volume (SRV) in the OH section. The objective was to create at least two to three multiple independent fractures in the OH section. The challenge was to manage the injection rates and deliver the diverter accurately to the bottomhole to create a bridge at the open fracture, isolate it, and initiate a new fracture. This paper discusses this process, and the the lessons learned during the treatment execution.
In addition to the description above, the following issues had to be addressed before progressing to the primary fracturing treatment: heavy mud was in the wellbore and OH section, this was a low-permeability reservoir, operator’s Christmas tree pressure rating was low, this was a deep well with a long OH interval, there was an extremely short operational execution deadline, and this well’s close proximity to an adjacent well, leading to possible communication between the wells.
This paper discusses the fracturing analyses performed to design the fracturing treatment, the ideologies used for performing the successful fracturing treatment using diverter technology, and the results achieved using this technique.
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Modeling of Shale-Erosion Behavior in Aqueous Drilling Fluids
More LessAbstractNumerous shale-stability issues can occur while drilling with water-based muds (WBMs), including shale sloughing and cutting disintegration. These issues can be detrimental to the formation and pose difficulties with respect to rheology control, possibly reducing the rate of penetration (ROP). A “shale-erosion test” is a well-known laboratory test used to characterize the erosion of cuttings in WBMs.
This paper documents a mathematical modeling tool known as an artificial neural network (ANN) used to model the erosion behavior of shale cutting in WBM. The ANN model establishes complex relationships between a set of inputs and an output based on computational modeling. For ANN modeling of shale-erosion behavior, the shale mineralogy and fluid composition constitute a set of inputs, while experimentally obtained “% erosion or % recovery” of the cuttings from the shale-erosion test represent the output.
Experimental data for building the ANN model was obtained by performing approximately 150 standard shale-erosion tests using five different shales with varying mineralogy and WBMs with varying salt concentrations/types, shale stabilizers, and mud weights. For every test conducted, the input data (shale and fluid characteristics) and the output data (% recovery) was incorporated into the ANN model. The ANN model was then run to establish relationships between inputs and the output, which exhibited excellent correlation with R2 ≈ 0.85–0.90. The ANN model was successfully validated for an independent set of shale-fluid interactions.
With the novel ANN model in place, erosion behavior of cuttings could be predicted in advance, thereby reducing the number of trials necessary in technical service labs. Mud engineers can use this model on a real-time basis as the shale chemistry varies with the depth of the formation drilling. The model could provide convenient measurement of fluid performance, enabling fluid optimization necessary to obtain desired shale behavior in advance, thereby minimizing drilling risks and costs associated with these oftentimes unpredictable shales.
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Optimizing Lateral Lengths in Horizontal Wells for a Heterogeneous Shale Play
Authors Larry Chorn, Neil Stegent and Jeffrey YarusAbstractA successful evaluation and development program in oil- and gas-bearing shales requires considerable analysis and investment, not to mention optimization to help ensure a profitable outcome. Accelerating optimization, reducing capital expenditures, and improving lifecycle net present value (NPV) for the asset are reasonable goals. Seven shale properties are key drivers to help achieve successful play economics. However, the heterogeneity of shales makes well location selection difficult without appraisal well logs and geostatistical mapping of shale property quality. The analysis method allows operators to quickly high-grade areas within a large, heterogeneous shale play using logging suites from a limited number of wellbores in the play. Further, the methodology has been extended to quantify the play’s potential reward versus risk distribution for in-fill drilling investments. This study extends the method to optimizing lateral lengths of horizontal wells. Geostatistics provides a means to determine correlation lengths of aggregate shale properties known to be critical to successful economics. The correlation length is used to determine the appropriate length of the horizontal well lateral, restricting it within the highest rock quality for stimulation effectiveness and production rates. Because optimal lateral lengths can be predicted using this approach, it is now possible to pinpoint the best wellhead location, the best landing point for the horizontal portion of the well, and set the optimal length of the lateral. This reduces the drilling of unproductive lateral lengths and targets stimulations. By shortening the “trial-and-error” evaluation lifecycle stage using this methodology, an operator can develop an asset more quickly and at less cost than with previous approaches.
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An Integrated Approach Towards a Holistic Sedimentological and Pore-Scale Characterisation of Fine-Grained (Shale) Unconventional Reservoirs
Authors K. Dasgupta and B. KosticAbstractFor a holistic characterisation of fine-grained unconventional reservoirs, our integrated approach utilises coherent, reproducible datasets and refined work practices carried out within a comprehensive quality management system. A typical reservoir characterisation includes integration of sedimentological, structural and pore-scale datasets, however, the specific work flow design depends entirely on the nature of the problem and the availability of appropriate data.
This paper illustrates an example of unconventional reservoir characterisation of a fine-grained formation from the North Sea where the specific aims were to establish the depositional framework for recognising sedimentary environments, recommend sample locations to target specific queries within the sedimentological context for petrographical and geochemical analyses, to investigate what porosity types are present and to assess ‘brittleness’ of the rocks.
First and foremost, high-resolution interpretative graphic core descriptions were carried out at 1:24 scale, utilising Badley Ashton’s mudrock-specific lithotypes and depositional packages schemes. Lithotype characterisation uniquely captures very fine-scale attributes (bed to subbed scale), whilst upscaled depositional packages (bed-stack scale) provide a more holistic characterisation from core, as well as from wireline and image logs, where available. Plugs coded by the above descriptors were selected post-logging, for detailed petrographical and geochemical analysis including Rock-Eval pyrolysis within the sedimentological/structural context. Mineralogical data was acquired by whole-rock and clay-fraction XRD analysis, whilst pore-scale fabric/textural investigation were undertaken by conventional light microscopy and BS-SEM. A subset of the plugs was subjected to FIB SEM analysis to characterise any potentially organic matter associated pore system. All these different strands of data were then integrated to evaluate and link the depositional system/sedimentary environment, storage capacity and brittleness of the reservoir in order to assess the overall reservoir potential of the fine-grained formation.
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World’s First Through-Tubing ESP Swap on Electric Line in Highly Deviated Wellbores
Authors M. Kuck, J. Albright and C. BlountAbstractElectric wireline and tractor equipment were chosen to perform through-tubing electric submersible pump change-outs in a remote location with limited access and equipment availability. Electric wireline was available on location where other rigless options such as coiled tubing could not be mobilized. This paper records the retrieval of through-tubing-conveyed electric submersible pumps (TTC ESPs) from three wells and their replacement in two of these wells using a highly adaptable tool string. The application of an existing tool implemented in a novel manner provided benefits to the operator and has potential applications for other operators maintaining through-tubing-conveyed ESPs in deviated wells. The pump assemblies were removed through tubing while the permanently installed equipment, such as seal, motor and cable, remained in situ. All wells contained three individual assemblies to be retrieved including a tubing stop, tubing packoff with check valve and knock-out pressure relief valve, and the pump assembly. The assemblies were re-installed in two wells and the wells placed back in production. The method described herein confirms electric wireline and tractor equipment as a viable alternative for rigless replacement of through-tubing electric submersible pumps.
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The Bowland Shale in the Roosecote Borehole of the Lancaster Fells sub-Basin, Craven Basin, UK: a Potential UK Shale gas Play?
Authors Edward Hough, Christopher H Vane, Nigel JP Smith and Vicky L Moss-HayesAbstractA re-evaluation of the Roosecote Borehole, located in the northern part of the Craven Basin (northern England), places the Bowland Shale in a modern geological context and allows an improved understanding of basin evolution and shale hydrocarbon prospectivity. In northern England during the Early Carboniferous, rapidly subsiding sub-basins developed between local highs in the Craven Basin. Subsequently, during the thermal relaxation phase, a period of regional subsidence allowed thick accumulations, locally in excess of 500 m, of hemi-pelagic mudstone to be deposited as a transgressive systems tract.
The Roosecote Borehole is a stratotype section for the Bowland Shale Formation, located close to the northern basin- to- shelf margin of the Craven Basin. The upper part of the Mississippian (Lower Carboniferous) Bowland Shale Formation is the principal potential shale gas play in the British Isles. The Bowland Shale and other argillaceous units of the Craven Group are rich in organic matter, have a similar depositional style to coeval units in the USA including the world-class Barnett Shale of the Fort Worth Basin, Texas, USA. Throughout England, Wales and Ireland it is currently being investigated by several exploration companies, with at least 4 dedicated shale exploration wells now drilled.
Rock evaluation indicates the TOC at between 1.73 – 3.72 %. Many samples indicate a mixture of type III and IV kerogens; there was no evidence for type I or II kerogens found. Thermal maturity for the sequence is within the oil window, with results indicating liquid oil and wet and dry gas have been generated. However, an estimate of the organic matter transformation ratio of 0.36 (36% kerogen conversion to hydrocarbons being possible) compares poorly to the Barnett Shale. Consequently we conclude that the Bowland Shale within the Roosecote Borehole has some, but possibly lower, potential as a shale oil play.
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Modeling Transportation Logistics, Water Use, and Surface Footprint for Shale Gas Field Developments
Authors Mathias Mitschanek, Gerhard Thonhauser and Michael ProhaskaAbstractOptimizing operational efficiencies in unconventional resource developments is one of the key success drivers for improved economics. In this work, an approach for exactly that problem is presented, designed for a field development scenario in Germany. Starting with a model that captures all key parameters which are influencing a development program such as the gas market and prize scenarios, political situation, environmental regulations, logistical requirements, etc., it immediately turns out that the highly complex model has to be significantly simplified and a sub-model with clear and precise boundary conditions has to be generated. This sub-model is tuned to problems of particular interest, considering technological parameters such as the impact of various state of the art drilling technologies or different fracturing methodologies on the entire development program. It is possible to identify interrelations of various procedures and allows estimating project costs. Operational scenarios can also efficiently be tested, and validated and the financial key parameters of different scenarios can be compared. Moreover, short- and long-term benefits and drawbacks of various solutions can be assessed and optimized. Also, limitations of System Dynamics for that kind of simulation are pointed out, and it is shown how to solve the problem with an Agent Based Modeling approach.
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Imbibition and Water Blockage in Unconventional Reservoirs: Well Management Implications During Flowback and Early Production
Authors A. Bertoncello, J. Wallace, C. Blyton, M. Honarpour and C.S. KabirAbstractDriven by field logistics in an unconventional setting, a well may undergo weeks to months of shut-in following hydraulic-fracture stimulation. In unconventional reservoirs, field experiences indicate that such shut-in episodes may improve well productivity significantly while reducing water production. Multiphase flow mechanisms were found to explain this behavior. Aided by laboratory relative-permeability, capillary pressure data, and their dependency to stress in a shale-gas reservoir, the flow-simulation model was able to reproduce the suspected water blocking behavior. Results demonstrate that a well resting period improves early productivity while reducing water production. The results also indicate that minimizing water invasion in the formation is crucial to avoid significant water blockage.
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Use of Near Bit Azimuthal Gamma Ray and Inclination Tool Improves Geosteering in CBM Wells, Airth Field, Scotland
Authors Nicholas Thwaites and Asong SuhAbstractInterest in European Coal Bed Methane (CBM), driven by an increasing demand for supplies of natural gas in Europe has been ongoing since the 1990’s in the UK, Belgium, Germany, France and Poland.
The nature of Carboniferous age European coals: multiple, thinner coal seams with lower permeability than coals seen in Australia or North America has resulted in a horizontal well or multi lateral wellbore architecture employing geosteering through the coal seams. Use of a conventional directional drilling Bottom Hole Assembly (BHA) in which the Logging While Drilling (LWD) sensors are usually 40ft or more from the drill bit, makes geosteering in structurally complex coals, with changing dip and rolling topography a major challenge. The cost sensitive nature of CBM wells makes the use of geosteering tools such as azimuthal resistivity tools uneconomic.
This paper describes the experience of Dart Energy and its heritage company, Composite Energy, in introducing an instrumented mud motor with a near bit Azimuthal Gamma Ray and Inclination tool as a cost effective geosteering aid on the Airth CBM Field in Central Scotland. The use of an instrumented mud motor enabled Dart Energy to improve geosteering performance, increasing net coal in each geosteered section, near doubling of average Rate Of Penetration (ROP), and reducing the number of time consuming and costly sidetracks.
The improvement in geosteering is a critical part of realising the commerciality of CBM wells producing from thinner, structurally complex Carboniferous age coals found in the UK and Northern Europe.
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Well Design Evolution Towards the First Commercial Unconventional Gas Flowrate in Europe
Authors Nicholas Thwaites and Lynne JamesAbstractThe demand for indigenous supplies of natural gas in the UK and other countries in Europe has driven operations in the unconventional gas arena since the 1990s. In Coal Bed Methane (CBM) there have been attempts in the UK, Belgium, Germany, France and Poland.
Dart Energy and its heritage company, Composite Energy, have been active in CBM in the UK since 2004, drilling 25 CBM wells in the UK, including 10 appraisal and development wells on the Airth field in central Scotland. A further 4 appraisal wells were drilled by the previous operator of the Airth field in the 1990s.
The local Carboniferous coal geology, as with most European coals of Carboniferous age, is characterised by thin, numerous, low permeability, undulating coal seams. A number of different well designs were tried over the 14 Airth wells to meet the challenges of the local geology: initially vertical fracture stimulated wells; moving to geosteered multi-lateral horizontal wells, either intersecting a vertical well at the end of the horizontal section or as ‘updip’ branches off a motherbore without an intersection and finally multilateral geosteered horizontal wells intersecting a vertical well at the start of the horizontal section.
The evolution in well design incorporated learnings from drilling operations, reservoir geology and production operations for each type of well architecture and advances in drilling technology in other CBM provinces around the world, adapting them to answer the particular subsurface problems encountered in the Airth field. Eventually, through this evolutionary learning process, Dart Energy was able to announce a commercial flowrate of 0.7MMscf/d from Airth 12 in January 2013, a multi-lateral horizontal well with a vertical well intersection at the start of the horizontal section.
This paper describes the journey to that success, charting the evolution of CBM production well design on the Airth field, recognising the geological factors that drive well design, an evolution that can be applied to Carboniferous coal systems with thin, numerous and structurally complex coal seams found in other parts of the UK and Northern Europe.
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New Sponge Liner Coring System Records Step-Change Improvement in Core Acquisition and Accurate Fluid Recovery
Authors Les Shale, Steven Radford, Thomas Uhlenberg, Jon Rylance, Audun Kvinnesland and Carlos RengelAbstractNew sponge coring service and technology have been introduced to the oil and gas industry. Admittedly sponge coring has been an industry offering in some form for over twenty years but until now it has been plagued by chronic problems. The objective of sponge coring was to determine separate in-situ oil and water saturations of the formation materials. The problem with conventional coring has always been that the fluids would be expelled and lost from the core by the expanding gas while bringing it to the surface. The long-time solution was to surround the core with a special oil-absorptive (oleophilic) sponge material that would capture the expelled oil and hold it in place for laboratory analysis. The challenge was to fit the sponge tightly enough around the core to prevent fluid migration and mud contamination in the sponge-core clearance annulus, and yet avoid core jamming and sponge damage.
This new, more accurate sponge liner coring service is now in place, showing excellent results. A balance seems to have been achieved between smooth core entry and a properly fitting, pre-saturated sponge with virtually no fluid migration. This new service cuts and provides oil-absorptive sponge-encased 3½-in. diameter core in 30 ft lengths with a maximum downhole temperature and pressure of 195°F (90° C) and 15,000 psi (1,034 bar) respectively. Special vacuum pump service equipment and sealing system are utilized to pre-saturate the sponge liner with brine.
In late 2012 a major operator utilized this new and previously unproven system to core nearly 300 ft of sponge core in New Mexico, USA. The coring program used a special low-invasion coring fluid with a low spurt loss and a staged trip-out-of-the-hole schedule to minimize gas expansion/oil movement. The precision core bit that cut a tight-clearance core provided exceptional results with an average rate of penetration (ROP) of 10.4 ft/hr, with 97% core recovery and observable oil saturation in the sponge, indicating the system worked as designed. This case study will be described in detail within this paper.
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