Fracture Diagnostics Results for the First Multiwell Experiment's Paludal Zone Stimulation

Abstract

A dual seismic system designed to monitor the growth of hydrofractures was fielded during the first stimulation at the U.S. DOE-sponsored Multiwell Experiment (MWX) during Dec. 1983. The MWX consists of three 8,OOO-ft [2438-m] wells drilled in low-permeability gas reservoirs. The wellbores are spaced less than 200 ft [61 m] apart over most of their length. With this configuration, microseismic activity created by the fracture treatment in one well could be observed with downhole geophone packages in the two adjacent wells.Responses of the two triaxial borehole seismic tools (BST's) were monitored in real time. Upon detection of a seismic event of known location, orientations of the BST's were determined from the polarization of the compressional wave arrivals. From knowledge of the horizontal and vertical angles of incidence and an empirical estimate of seismic velocities, the locations of the fracture-induced seismic sources were estimated. Thus the location of the microseisms could be estimated and, in turn, the fracture height and extent inferred.This paper presents the results of fracture diagnostics by use of this borehole seismic system for the first MWX stimulation. This information is compared and combined with the results obtained from other diagnostic techniques to provide an integrated estimate of the fracture geometry resulting from the stimulation.

Influence of Fracture Toughness on the Geometry of Hydraulic Fractures

“…Recordings of microseismicity associated with hydraulic fracturing reveal that most of the events appear to be shear events in the rock on either side of the fracture, not tensile events at the crack tip (see Hart et al 28 for references). Such shear events can' be related to a scale effect as described previously, but the increase in pore pressure as a result of fluid loss may also contribute to such behavior.…”

In-Situ Stresses in Low-Permeability, Nonmarine Rocks

“…21,22 The subject of this paper is twofold: (1) a compendium of all of the in situ stress measurements conducted in nonmarine rocks at the Multiwell Experiment (MWX) in the Piceance basin of Colorado and (2) a critical analysis of the techniques, the results and the implications. This study builds on tnany previous stress measurements and analyses at this site, 8,10,11,13,20,21 The MWX experiment23 is a Department of Energy funded experiment to characterize low-permeability reservoirs in the western United States and to test technology for the production of natural gas from these marginal resources. The site is located in the Piceance basin in west-central Colorado near the town of Rifle.…”

Use of Long-Period Seismometers To Determine Induced Fracture Geometry

“…Changes in LP signal pulse duration coincident with treatment conditions required to create additional fracture volume suggests that information about induced-fracture dimensions may be embodied in the spectral content of these signals. 4. Coincidence of most LP signals with times when injection pressure exceeds minimum closure stress, minimum stress to create additional fracture volume, and rapid shut-ins strongly suggests a causal relationship between injection pressure and the origin ofthe LP signals.…”