Abstract

Treating pressures from refracturing treatments and simulations of horizontal stress changes due to production suggest that the initiation of the refracture plane will be normal to that of the initial treatment. This possibility makes more wells candidates for refracturing.

Introduction

A review of a number of refracturing treatments was made to determine what insight could be obtained from their treatment pressure histories. The effect of the previous proppant and the stress changes due to pore pressure depletion were of particular interest. Comparing the pressure histories of the treatments led to some observations and theories on the role played by reservoir pore pressure in refracturing treatments.

PORE PRESSURE GRADIENTS AFTER PRODUCTION

A successful refracturing treatment is one that creates a fracture having higher fracture conductivity and/or penetrating an area of higher pore pressure than the previous fracture. There can be significant horizontal pore pressure gradients in the reservoir due to the production after the initial fracture treatment, which will affect the treating pressure of the refracturing treatment.

Figure 1 shows a schematic of pressure contours around a well with a relatively short effective fracture (100-200 ft) due to either short actual penetration of the proppant or some damage to the fracture conductivity of a longer fracture reducing its effective penetration. A transient well test analysis will indicate this short effective fracture length, making this well a candidate for refracturing. The refracture treatment should be designed to achieve penetration into the reservoir with higher fracture conductivity. This is the scenario assumed for most successful refracturing treatments.

Pressure contours around wells having fractures with high or infinite acting conductivity and penetrating more than fifty percent of the assigned drainage radius are shown in Fig. 2. With our present knowledge of fracturing, which assumes that the plane of the new fracture has the same azimuth as the previous fracture, these wells are considered poor candidates for refracturing. Better reserve recovery can be obtained from infill drilling and fracturing the new wells.

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