A Fracturing Technique To Minimize Water Production

Abstract

Abstract A major problem in stimulating some formations has been the high production of formation water following fracturing treatments. This is generally considered to be due to the lack of a sufficient barrier to help prevent downward growth of the fracture from the hydrocarbon producing zone into the water producing interval. Thus, with conventional treatments, the undesirable water producing zone may be fractured and propped producing zone may be fractured and propped during the fracturing treatment of the hydrocarbon producing zone. A density controlled fracturing technique has been developed that is capable of placing the proppant in the upper portion of a producing zone. The technique utilizes a high producing zone. The technique utilizes a high density pad followed by a lower density treating fluid containing the proppant. This sequence allows the proppant to be preferentially placed in the upper portion preferentially placed in the upper portion of a vertical fracture. Laboratory tests have been conducted with a fracture model that demonstrated layering of fluids of different densities. Field results of several density controlled fracturing treatments are presented. Results demonstrate that this method is capable of increasing hydrocarbon production with little or no increase in the production of formation water. Introduction Water producing zones are often closely associated with hydrocarbon bearing formations. In some cases, the water is separated from hydrocarbons by a barrier, while in others there is no separation and the two phases are in direct contact. When hydraulic phases are in direct contact. When hydraulic fracturing is used to stimulate hydrocarbon bearing formations that are in direct contact with water, the fracture very likely will penetrate into the water bearing zone. The penetrate into the water bearing zone. The Edwards Limestone Trend of South Texas is an example of such a formation. The Edwards is approximately 1,000 feet (305 m) in thickness with hydrocarbon accumulations occurring near the top. Even when the hydrocarbon producing formation and water are separated by a third zone, a hydraulic fracture may grow out of the producing zone, through the separating layer, and into the water producing interval. Whether or not this will occur may depend on the type and thickness of the formations and the type of fracturing treatment employed. Conventional stimulation techniques on these types of formations often result in high volumes of produced water. Water production may be high immediately after production may be high immediately after the treatment, or the well may gradually water out over a period of a few weeks or months. CONVENTIONAL FRACTURING TREATMENTS When relatively low viscosity fracturing fluids such as uncrosslinked guar or cellulose are employed to stimulate formations, an equilibrium bed height of proppant is deposited in the bottom of the proppant is deposited in the bottom of the fracture. In instances where the fracture penetrates a water producing zone, the lower water zone may receive a large amount of proppant (Fig. 1). Gamma ray logs run before and after a treatment of this type indicated proppant some 35 feet (10.7 m) below the bottom perforation (Fig. 5). When high viscosity systems such as emulsions or crosslinked gels are utilized as fracturing fluids, proppant settling may be greatly reduced or eliminated. In this instance, the proppant is essentially distributed from top to bottom of a vertical fracture as shown in Fig. 2.