Abstract

Hydraulic Impedance Testing (HIT) is a technique which has been developed to measure formation fractures intersecting wellbores. Fracture dimensions are determined by introducing a pressure pulse into a well and interpreting the resulting pressure trace. The method only involves the use of wellhead equipment and is therefore a very cost effective method for obtaining information about fractures in the formation. This paper describes a method for interpreting HIT data and demonstrates its validity through laboratory and field measurements.

Direct comparisons between HIT field measurements and independent evidence for fracture dimensions are presented for a number of water injection wells. The most striking results are that HIT estimates of fracture height correlate well with the flowing intervals obtained from spinner logs, and HIT estimates of fracture length tend to agree with those obtained from PFO's. HIT derived fracture dimensions are also comparable to those obtained from computer simulation of thermal fracturing.

More than 50 water injection wells have been tested with HIT and found to be intersected by formation fractures. Determination of fracture geometries in water injectors can be used for the optimisation of both areal and vertical waterflood sweep and increase understanding of the processes controlling injectivity. HIT may also provide a useful tool in hydraulic fracturing work.

Introduction

Hydraulic Impedance Testing (HIT) is a technique for detecting and measuring formation fractures which intersect wellbores. BP adopted HIT to help identify the processes governing water injection and consequently this paper will concentrate on the application of the technique to water injection wells.

Although waterflooding has been routinely applied, water injection was assumed to be a simple process and, until recently, no real efforts were made to understand the underlying mechanisms. In many instances water was assumed to be injected through the fixed sand face area surrounding the perforation tunnels and to flow radially into the formation. Core flood tests showed significant reductions in permeability after a relatively short time, when flooding with anything other than very clean water. To protect injection capacity, it was therefore seen as vital to protect the sandface from blocking and this led to the need for high quality injection water.

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