Far East Hydrocarbons 2016

Astokh area of Piltun-Astokhskoye oil-gas condensate field (Astokh field) is one of the oil assets of Sakhalin Energy Investment Company Ltd. (Sakhalin Enegy). The field has seventeen years of production history and currently has being developing under water flood scheme. It still has significant reserves to recover and at the current stage of the field development main focus is put on further infill drilling and water injection optimization. Full-field integrated modeling with realistic range of subsurface scenarios is an essential tool for optimizing further field development strategy and maximizing the value of the asset.

In the presence of long production history, 4D seismic and surveillance data reservoir model construction work cannot be efficiently done without integrated approach where all relevant disciplines provide their input to the final product. This paper describes reservoir modelling work that has been recently done in Astokh field. Multi-disciplinary team of petrophysicist, geoscientists and reservoir engineers of Sakhalin Energy has made an effort to combine all available information for constructing a brand new Astokh integrated model with in-depth reviewing of petrophysical and geological aspects in close connection with reservoir engineering data and reservoir simulation modelling.

The main oil production object design U1-2 of field Kraynee drilled on various development systems. This geological object is currently under active development for the period 2012–2015 drilled 126 wells. Due to the small oil-saturated thickness and low permeability reservoir of the object from the drilling of directional wells has moved to drilling horizontal wells with multi-stage fracturing conduct in the development and direction of different horizontal sections. Analysis of the efficiency of reserves recovery on units with different systems of development have shown that a clear advantage of any system the location of wells for the Jurassic sediments have not been identified.

In the report, we explain the geophysical causes of variations in the spectrum of natural microseisms. We describe the mathematical methods of extracting information from microseismic fields about geological structure, including the presence and position of hydrocarbon deposits. We present examples of solving different geological and technological problems of the oil and gas industry by microseismic methods both onshore and offshore

Conclusions:

-The QI-PP technologies are employed in Sakhalin Energy for several purposes, e.g.:

• o For seismic 4D monitoring in regards to changes in pressure (depletion/ injection), or in saturation or fluid types (water front, gas cap presence/extension). Therefore, the elastic rock properties were defined to predict the seismic response away from well control, and 1D and 2D synthetics were generated and studied for important reservoir settings.
• o For fluid type appraisal, e.g. oil-water contacts in development targets or for thin oil rim detectability.

-Sakhalin Energy Petrophysicists are receiving training on the QI-PP-technologies by the in-house QI-PP specialist. That training is intended to allow the Petrophysicists to conduct QI-PP technologies by themselves in the future (co-assess the feasibility of upcoming 4D campaigns and support the 4D-interpretation and de-risking of Sakhalin Energy’s development targets).

Some results:

The geomechanical analysis on recently acquired cores in both the Lunskoye and Astokh assets allows defining how effective pressures alter the seismic velocities. These results will be included to support predicting the effects of pressure changes by injection and depletion on seismic data, quantitatively.

Recent QI-PP studies demonstrated that residual or migrating gas is present in the LUN aquifers and that the oil rim is seismically barely visible.

The Li and Yuan (2001) approximation showed to be, in previous works, the most general and stable approximation created so far to perform the velocity analysis. For this reason its limitations were studied aiming to understand which kind of model could affect the quality of the results obtained with this approximation. It was previously studied about how a strong velocity increase and decrease could affect the quality of the curve fitting. However, in this work, we must test how the velocity decrease influences the quality of the velocity analysis once it was observed that the velocity decrease generates more difficulty to the procedure with the Li and Yuan (2001) approximation.

The multicomponent seismic presents a more complex wave field than the conventional seismic, for this reason it has been used in seismic survey. For the offshore situations, there is the necessity of use OBN (Ocean Bottom Nodes) technology to obtain S wave informations. These technologies generate nonhyperbolic events due to the ray trace asymmetry, resultant from the difference between the angle of incidence and angle of emergence (for wave conversion), and datum difference between source and receptor (for OBN technology). This kind of event is also found associated to the use of SWD (Seismic While Drilling) technology which is important to reach informations of ultra-deep reservoirs, where usually has informations with low amplitudes. The focus of this work is to perform the velocity analysis of converted wave events, acquired at different depths, following an inversion routine by an optimization criterion. Thus, it will be possible to infer if the method is applicable and understand its behavior.

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The unified regional seismogeological section (Megaprofile) through the bulky structural elements of basins was drafted as a result of research. It has been the first generalized work for more than 40 years of geological and geophysical researches of Okhotsk and Japanese seas. Based on seismostratigraphic interpretation and well data results Megaprofile was transformed into regional composite lithologic and stratigraphic section where we can trace rocks composition change in different sedimentary basins. Analysis and generalization of the latest regional geodynamic reconstrustion results with the verification of extensive factual material may contribute to the revaluation of oil and gas potential of the acoustic basement rocks, and the huge in size positive structures with the proposed large crust of weathering may be the new hydrocarbon direction in region.

In areas with an active tectonic past, the analysis of the sealing properties of faults is an important aspect both for the understanding of HC migration pathways from the source rock into the trap and for the evaluation of the internal trap structure and integrity. We present a workflow, which utilizes the whole amount of well and seismic information to evaluate the key factors on which the fault seal properties depend.

Our approach includes detailed structural interpretation using special seismic attributes, restoration of the tectonic history, mapping of indications of vertical fluid migration from seismic data. We also create a detailed 3D lithological model based on the results of seismic inversion, from which attributes like Juxtaposition and SGR can be extracted. The advanced use of the seismic data makes the workflow also applicable in areas with sparse well control.

The presented workflow helps to mitigate the risk at each stage of the E&P process. It results in a more realistic understanding of reserves distribution and hydrocarbon retention in faulted traps, including the potential allocation of additional reserves in undrained blocks. It should also lead to a better planning of the number and location of wells to be drilled.