Abstract

Hydraulic proppant fracturing is one of the most effective tools to optimize production in the mature, low- permeability reservoirs found in the Pannonian Basin in Central Europe. Fracturing can effectively enhance production by improving reservoir contact, but for wells already producing with high water cut, even a small fracture extension into a water-bearing or "wet" zone offsets the gains in hydrocarbon production. Fracture geometry control (FGC) techniques limit increases in water cut, which is one of the greatest challenges to extending economic production and maximizing ultimate recovery for mature wells. Artificial barrier placement and proppant channel fracturing were proven to improve hydrocarbon production while fracturing stimulation targets adjacent to high water saturation intervals.

The pilot included candidates in thin, low-permeability sandstone reservoirs, located within 5 to 10 m of wet intervals. An integrated engineering approach to fracture height growth was applied, including a new proppant transport model to predict fracture geometry improvement using the FGC solution. The FGC solution consisted of injection of an engineered particulate mixture designed to bridge at the fracture edges and arrest height growth. Additionally, the bridging mixture provided reduced conductivity and acted as a fracture flow restriction for water. The FGC solution was also combined with channel fracturing in some trials as an attempt to reduce net pressure development, minimize the risk of height growth and improve fracture quality in the low-permeability reservoirs. The new engineering approach, incorporating the new solids transport simulator, enabled the successful implementation of the FGC technique in the pilot candidates. Fracture height control was achieved in absence of good geological barriers. The benefits of this new approach are supported by a consistent improvement in hydrocarbon production without an increase in water cut. In field A, the combination of FGC and channel fracturing resulted in additional production when compared to wells where only FGC was implemented. Evaluation of this pilot included a comparison with offset wells stimulated without this technique when a water cut increase was always observed in the field A.

This paper describes the first implementation of the complex technology and engineering solution to control fracture height for conventional wells in the Pannonian Basin. For the first time, the mixture of solids was modeled directly, and the influence on fracture geometry and production results is shown. The cases are of significant interest because of the global challenge of maximizing recovery from mature reservoirs with nearby water hazards. The application of a full engineering process for the design, placement, and evaluation of the fracture height control treatments provides an improved degree of confidence that such operations can result successful production optimization. The workflow as presented and applied is an effective tool to reduce risk of high water production when fracturing close to water contacts.

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