A Study On Fractures In Qom Formation In Kashan Block, Central Iran Basin

Aran structure zone located in the north of Kashan Block is the main prospect in Kashan Block. As for geological structure, this anticline is at the joint of the main Central Iran Basin and Kashan Depression which is a southwest secondary structure. Iran anticline is the most important oil and gas bearing trap in this structural zone, even within the entire Kashan Block. Marine Qom Formation deposited in the back arc basin during Tertiary(Oligo-Miocene) is the exploration target which is a known fractured reservoir. C₄ sub-member of Qom Formation is the main pay formation.The most salient problem of carbonate fractured reservoir is the very intense inhomogeneity. The accurate description and prediction for fractures is the key to exploit effectively for carbonate hydrocarbon reservoir. Among them, quantitative characterization of the fracture parameters and quantitative prediction of distribution of fracture void is one of the most difficult problems.This paper conducts a systematical study on fractures in Qom Formation of Aran anticline synthetically using outcrops, cores, logging data, and 3-D seismic data. The development characteristics and distribution law of fractures were studied based on similar outcrops observation, cores, investigation on imaging logging data, and parametric statistics. Under the constraint of imaging logging data, the method of interpreting fracture parameters of Dual Lateral Log(DLL) was used to invert fracture parameters quantitatively and analyze where the favorable members of fractured reservoir are. Under the constraint of cores, outcrops and fractural parameters of inversion, and on the basis of accurate description on structural feature, the method of Void Space Description(VSD) was used to calculate pore space of fractures associated with fault quantitatively, and to describe the development distribution characteristics in C₄ sub-member of Aran anticline. Main understanding and results obtained are as following:1. Fractures are controlled by both of folding and faulting in Qom Formation in Kashan Block.2. There are 3 complex fracture systems in plane in C₄ sub-member of Aran anticline.3. The method of Void Space Description(VSD) was used to calculate pore space of fractures associated with fault quantitatively in study area, and yielded good results.4. The buckling position of minor fault-drag fold is a favorable location for drilling.