oa Thermal Simulation for a Shallow Limestone - Rubble Reservoir in Bahrain Field

Rubble Limestone is the descriptive name given to a massive Limestone unit of the Mishrif formation,<br>in middle Cretaceous in age. The zone consists of two layers are eroded in the crestal part of the<br>structure. Large volumes of oil are trapped against the Blue shale at the up structure. The zone has<br>both heavy & light oil. The amount of Heavy oil is estimated to be 90% of the initial oil in place.<br>Currently only light oil is being produced. This paper highlights the studies to evaluate Heavy oil<br>production potential.<br>Two separate studies were carried out, the first was to describe and characterize Rubble in order to<br>map the light & heavy oil and the water bearing layers. Geostatistical methods were used to populate<br>the 3D model of the reservoir with porosity & permeability values. After obtaining an estimate of the<br>areas of heavy and light oil, a fresh study was initiated to review and evaluate the Heavy oil prospect<br>and to prepare a suitable thermal EOR pilot plan for the heavy oil recovery. The study included<br>numerical modeling and simulation of a pilot area and find out the suitable EOR process and design the pilot.<br>The study indicated that the reservoir has too low matrix permeability and very small fracture volumes<br>to allow steam chamber formation. SAGD mechanism was therefore found not efficient for this<br>reservoir. Cyclic Steam Stimulation (CSS) has been simulated using two wells in the pilot area and<br>found attractive. Cold production from six different Horizontal wells were simulated and tested. They<br>indicated that cold production followed by CSS will be efficient to recover the Heavy oil. The paper will<br>describe the results of the study which led to drilling of the Horizontal pilot well for Cold production to<br>be followed by CSS Thermal process.