Refinement of Sand Dispersal Pattern in Deltaic Environment Using Multimineral Log Processing & Multiattribute Analysis - A Case Study in Nardipur Low, Cambay Basin, India

N. S. Dangwal, Swarup K. Mohanty, D. Manna, Birbal Singh, and Narendra K. Verma
INTEG,GEOPIC, ONGC, Dehradun, India

The Nardipur 3D area of Cambay Basin lies between Kalol and Limbodra fields covering the major low axis of Nardipur syncline. Sands within the Kalol Formation of Eocene age are the main producers of hydrocarbon in the area. The study area is falling in the delta plain environment, traversed by distributary channel network commonly representing channel bars, point bars ,crevasse splays etc.

These channels are having very limited width, to the tune of 200 to 300 m.The axial part are having good quality thin to moderate sand development while the facies deteriorate towards the banks. The abandoned channels had prevalent marshy and swampy environments marked by coal & carbonaceous-shales.

The sand of K-IX unit which is the main producer here is very thin in nature, of the order of 2~6 m and is capped by coal, occasionally with a thin intervening shale layer. This sand has developed variable porosity and is invariably found to be differentially charged, almost at all the places. The entrapment is basically strati-graphic and occasionally strati-structural in nature.

The production behaviour depends upon the reservoir properties, mainly porosity. The computation of effective porosity for sands after eliminating coal effect was very precisely carried out using multi mineral log processing. The processed logs were used as input for the Inversion and multi-attribute analysis (EMERGE).

The effective porosity model thus arrived at after the analysis, has clearly brought out the different parts of meandering channel system viz switching channel pattern, levees, point bars, crevesse splays with amalgamated sand forms etc. and the distribution pattern of the better porosity pods, validating the existing well results.
The study has opened up potential areas for exploration.

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