Geomechanical Analysis and Sand Production Prediction in Development Well, Case Study in Bunyu Field

Abstract

One of problem in oilfield development is sand production problems. This problem lower the productivity and cause unnecessary operation expenses due to damaged production facilities. In Bunyu oilfield, this problem often occurred in shallow zone at depth below 1750 m with sand content between 1 to 48%. Thus, the sand production prediction is required to prevent this problem occurs.
In geomechanical views, sand production problem occurs when the rock strength is fail to hold formation integrity caused by tensile force induced by fluid flows out the reservoir. In the research area, shallow zone tends to have lower rock strength due to lack of overburden resulting less consolidated formation than deeper zone. In this research, the geomechanical analysis is conducted to characterize the reservoirs layer with sand production problems and define critical drawdown pressure.
This research successfully define and classify the reservoir that prone to have sand production problem. The reservoir can be classified to three class based on rock strength values. By applying the critical porosity concept, the sand production phenomenon can be described by condition when the formation have low rock strength below critical value at critical porosity and enters the suspension state. In this state, rock strength mainly supported by pore fluid while in consolidate reservoir the formation integrity mainly supported by grain & matrix. Clean sand porosity model shows that the critical porosity in this area is 33.7 % with rock strength values as low as 15 MPa. From this model also known that the rock strength decrease along with increasing porosity. Drawdown pressure is one of external factor that can interfere and decrease the formation integrity. The maximum drawdown pressure are equal to difference between reservoir rock strength and critical rock strength. By quantifying appropriate minimum rock strength, the drawdown pressure can be optimized to avoid sand production occurs.