Influence of Non-parallel SAGD Well Pairs and Permeability Heterogeneities on Recovery Factors from Warm Heavy Oil Reservoirs

Abstract

A key component influencing the final recovery factor of a Steam Assisted Gravity Drainage (SAGD) well pattern is the correct well placement. The optimum spacing and position of the well pairs within the net pay is a function of in-situ oil viscosities, reservoir properties and heterogeneities defining the steam injectivity and the effective heat transfer within the reservoir.The well design parameters are typically optimized with thermal reservoir simulators constructed considering that both injector and producer wells are parallel to themselves, to the formation boundaries and with the well-pairs aligned throughout their entire length. However, due to various operational realities including the precision of the guiding tools that navigate the wells, actual SAGD well pairs in the field are seldom drilled perfectly parallel.The study was directed to wells drilled in thick, heavy oil reservoirs where the combination of very high permeabilities of poorly consolidated sands and reservoir temperatures higher than about 30 o C [86 o F] have the ability to flow cold at reasonable oil rates in spite of having in-situ oil viscosities in the thousands of centipoises. This paper expands the previous work of the authors (2010) analyzing the fact that wells from a SAGD pair in the field are not likely to be precisely parallel and quantifies the effects that this lack of exact parallelism brings to the production rates and overall recovery factors comparing them to the recovery variations that result from small to moderate reservoir heterogeneities.