Flow modeling and permeability estimation using borehole flow logs in heterogeneous fractured formations

Abstract

A numerical model of flow in the vicinity of a borehole is used to analyze flowmeter data obtained with high‐resolution flowmeters. The model is designed to (1) precisely compute flow in a borehole, (2) approximate the effects of flow in surrounding aquifers on the measured borehole flow, (3) allow for an arbitrary number (N) of entry/exit points connected to M < N far‐field aquifers, and (4) be consistent with the practical limitations of flowmeter measurements such as limits of resolution, typical measurement error, and finite measurement periods. The model is used in three modes: (1) a quasi‐steady pumping mode where there is no ambient flow, (2) a steady flow mode where ambient differences in far‐field water levels drive flow between fracture zones in the borehole, and (3) a cross‐borehole test mode where pumping in an adjacent borehole drives flow in the observation borehole. The model gives estimates of transmissivity for any number of fractures in steady or quasi‐steady flow experiments that agree with straddle‐packer test data. Field examples show how these cross‐borehole‐type curves can be used to estimate the storage coefficient of fractures and bedding planes and to determine whether fractures intersecting a borehole at different locations are hydraulically connected in the surrounding rock mass.