ABSTRACT

ABSTRACT

We have developed a new wireline hydrofracturing technique for in situ stress measurement which eliminates the need for drill rig and drill rod and renders the tripping of the straddle or impression packers continuous, fast, and inexpensive. Wireline conductors facilitate the use of downhole pressure transducers. We have confirmed the suitability of the new technique by testing it in a deep hole near the Monticello Reservoir, South Carolina. Our measurements indicate two local stress fields, one of them apparently linked to the impoundment-related induced seismicity.

INTRODUCTION

We have developed a new hydrofracturing field technique which renders the measurement of in situ stress considerably faster and less expensive. The major improvement is the conversion of hydrofracturing from a drill rod to a wireline method using two flexible hoses, one for packer inflation and another for test interval pressurization. The newly designed fracturing tool accommodates downhole pressure transducers connected to surface power supplies and recorders via the wireline conductors. Measurements previously conducted by necessity on the surface, now are carried out at the depth of interest. The drilling rig has been replaced by an easy-to-assemble tripod and a hoist located in a specially equipped truck. Hydrofracture delineation and orientation are determined by a wireline impression packer and orienting tool. The tripping of the hydrofracturing probes is now continuous and fast. Depths previously reached in hours are now arrived at in minutes. The wireline hoist truck can be used for conducting other geophysical logs in the hole. The system developed is similar in principle to that of Rummel et al [1983] but differs in many of its details. We have employed the new system to carry out stress measurements in Mont-2, a previously tested 1.1 km hole in the area of induced seismic activity near the Monticello Reservoir, South Carolina. The objective of our tests were: (1) to evaluate the suitability of our newly designed wireline hydrofracturing system for conducting stress measurements in deep holes, and (2) to obtain additional stress magnitudes and previously unavailable stress directions at different depths in the hole, and relate them to the local seismicity which was apparently induced by the reservoir impoundment. Details on the equipment and tests are given in the following sections.

Figure 1. Wireline straddle packer system. (available in full paper) Figure 2. Wirelide impression-orienting tool system. (available in full paper)

WIRELINE HYDROFRACTURING

The new hydrofracturing system consists of two major downhole tool assemblies, a wireline straddle packer and a wireline impression-orienting tool. Each is tripped into the testhole on a 7-conductor wireline operated by a hoist mounted on a logging truck. A tripod over the hole collar facilitates equipment tripping. Figure 1 and 2 are schematic diagrams showing the main mechanical, hydraulic and electrical components of the two downhole assemblies, the use of which will yield both stress magnitudes and directions in a hydrofracturing test.

Straddle Packer

The wireline straddle packer system is the downhole hydrofracturing tool and consists of three major components, straddle packer, pressure transducer housing, and pressure relief valves (Figure 1). The tool is linked mechanically and electrically through a cablehead to a 7- conductor wireline.

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