Evaluation of wireline formation testers in thinly laminated reservoirs

Abstract

Reservoir formations are complex, heterogeneous, and anisotropic. The distribution of both horizontal and vertical permeability strongly affects reservoir performance and the amount of hydrocarbon recovery. Early in the life of a reservoir, the main concern is the average effective horizontal permeability to oil or gas since this controls the productivity and completion design of individual wells. Later on, vertical permeability becomes important because of its effect on gas and water coning as well as the productivity of horizontal and multilateral wells. This is the reason why numbers of measurement are needed for a full reservoir description. However, different scales of measurement can result in different kh, kv and anisotropies. This thesis studies the effect of reservoir heterogeneity, focusing on discontinued shale barriers, on different pressure transient tests, namely, single probe WFT, dual packer WFT, and conventional well test. The study is done by varying shale barrier properties such as shape, amount and distance between shale barrier and the well bore and simulating pressure responses from the three types of pressure measurement using a reservoir simulator. Then, using pressure transient interpretation software to estimate reservoir parameters, such as horizontal and vertical permeability, permeability anisotropy, and radius of investigation from derivative plots. From the study, the effect of shale barriers can be seen as hump in derivative plots of single probe and dual packer WFT. For well test, the scale of effect is so small and hardly observed. Furthermore, variation in distance between shale and the well bore, and shape of shale can result in different characteristics of hump in the derivative plot. However, the variation in amount of shale does influence the hump in derivative plots.