Hydraulic Impedance Testing (HIT) is a technique for detecting and measuring formation fractures intersecting wellbores. A pressure pulse is introduced into a well and the resulting pressure trace is interpreted to give fracture dimensions. The initial part of this paper describes how HIT can be used to estimate fracture dimensions and presents some results from a laboratory experiment which show that dimensions can be accurately measured using HIT. The remainder of the paper describes field examples of the application of HIT. This includes a demonstration of how HIT traces change as pressure is reduced, which provides a method for determining fracture closure pressure.
The presence of fractures which enhance well productivity or injectivity can dramatically improve oil field profitability. It is therefore important to understand how fractures behave so that fracture designs and production strategies can be optimised.
Hydraulic Impedance Testing (HIT) is a technique for detecting and measuring the size of fractures which communicate with wellbores and can therefore be an important tool in the drive to improve understanding of fracturing and to monitor fracture growth.
HIT uses the transient response of the fluid in the wellbore and fracture which results from the introduction of a pressure pulse into the well to provide information about the fracture. The principles behind the technique are not new. In the 1960's Anderson and Stahl reported changes in the period of fluid oscillation in a wellbore as a fracture formed. In the 1980's Holzhausen published several papers detailing a form of HIT, although the methodology for analysing the pressure traces differs from that used for the work covered in this paper.
The method reported here provides estimates of both fracture height and fracture length. This can provide a useful addition to the tools available for fracture measurement, particularly in the design of hydraulic fractures where the engineer often has a good idea of fracture face area, with a relatively poor estimate of fracture height.
This paper starts by describing the methodology which has been developed for estimating fracture dimensions. The results of a laboratory study which show that HIT accurately measures known fracture geometries follows. Field investigations of fractures opening and closing using hydraulic impedance testing are then presented.