Determination the Effect of Pore Pressure Variation Due toDepletion of a Reservoir on Regional Faults; a Case Study

Different changes may occur in a reservoir during its production life. Study of these changes has an important role in upcoming operations. The influence of depletion on the frictional equilibrium is one of the items should be studied. Pre-existing faults and fractures will slide in regions there is no frictional equilibrium. Equilibrium may be lost due to depletion. Casing shearing or lost circulation may be occurred due to faulting and wells will be in their instable states. It is important to predict the effect of pore pressure changes and depletion on frictional equilibrium. Estimation of necessary time to create faults can be very helpful in production or in drilling new wells. It is possible to maintain the stability ofwells by avoiding fault sliding. Predicting the in-situ stresses is the key parameter to study the state of faults during the reservoir life. Different models are suggested in which decrease of horizontal stresses are predicted as function of pore pressure variation. In this article, two models are used to predict the variations of the in-situ stresses. The models are based on poro-elastic theory and theory of inclusions andboundary element. The effects of pore pressure variation are studied in a real reservoir. In the first step,Mechanical Earth Models of the reservoir is built using logging and coring data. Pore pressure variation is simulated as function of time for the reservoir life. In the reservoir the potential depth of fault sliding is analyzed and required time for faulting in that depth is predicted. It is feasible to gain more accurate redictions to use the second model to consider different important factors such as reservoir geometry.

Keywords:

Pore pressure , Depletion , MEM , BEM , Production , Stress variation