CARBONATE FRACTURED RESERVOIR CHARACTERIZATION USING ANALOGUE OUTCROP STUDY OF THE RAJAMANDALA CARBONATE COMPLEX, WEST JAVA

摘要

In general, carbonate reservoir show dual porosity behavior indicating highly heterogeneous due to influence of various secondary processes such as depositional facies and diagenesis. The occurrence of fractures as secondary porosity can add to more complex behavior of their performance. Therefore, understanding relationships among these secondary parameters is very important in order to model porosity and permeability distributions as well as to calculate volumetric resources. The main objective of this paper is to show results of an outcrop scale study of the relationship between fractures and carbonate facies in the Rajamandala Carbonate Complex (RJM). This work was supported by study of full length core descriptions from four shallow drilling conducted in the area namely ITB-URC-1, ITB-URC-2, ITB-URC-3 and ITB-URC-4 respectively.Fractures measurements and characterizations were conducted using scan line methods in several locations particularly concentrated near major faults and fold axis. More than 250 thin sections were evaluated to support outcrop scale study particularly in evaluating evidence of diagenesis process. Four main fractures are investigated in this study. These are shear fractures (faults), extension fractures, veins (calcite filling extension fractures) and stylolites.The results of the study show that fractures distributions and characteristics strongly dependent on carbonate facies. Data analysis indicates both fracture spacing and length followed power law distributions. The statistical analysis show the average R of fracture spacing is ranging between 0.85-0.97 meaning the data showing excellentcorrelation coefficient. The study indicates that small scale fractures form an important part of the overall porosity. However, fracture density is also clearly confrolled locally by the presence of faults and folds. In these areas, fracture density can be significantly higher in the vicinity of the faults and along the fold axis. Secondary processes such as dissolution along stylolites surfaces due to the groundwater interactions have also played major important roles in enlarging fracture apertures (vuggy porosity).