Horizontal well case study under pattern waterflood. Investigation of horizontal well performance in a heterogenous carbonate oil reservoir.

Abstract

The performance of two horizontal wells drilled in a major limestone oil reservoir in the Middle East was investigated. The wells were drilled to test the application of horizontal wells in the reservoir by replacing two watered out vertical wells.The reservoir is relatively thin (-45ft.) and highly heterogenous. The reservoir is characterised by significant vertical variation in horizontal permeability with the majority of the flow capacity situated in the botton 10-15% of the reservoir section. Furthermore, a thin, and possibly continuous, low vertical permeability dense calcified zone, caused by stylolitisation, has been suspected immediately above the high flow capacity formation.The Well A case is unique in that water breakthrough was observed in the vertical well, but to date, not in its replacement horizontal Well A (drilled in the upper half of the reservoir section). This is in spite of more than 24 months of production from Well A. This compares to the performance of the Well B replacement horizontal well in a nearby pattern where water production was recorded immediately after the well was brought on line.The performance of horizontal Wells A and B can be explained by examining the degree of vertical heterogeneity and layer segregation within the reservoir. The predicted shape and rate of advance of the water flood front in the Well A and B pattern element models can be successfully controlled using a combination of vertical layer heterogeneity and layer kv reduction. Specifically, it is layer permeability thickness product contrast and layer segregation that controls the shape of the advancing flood front. The greatest influence on well performance is observed when the vertical permeability of the dense calcified zone is drastically reduced.