Performance of Hydraulic Fractures in High Permeability Formations

Abstract

Abstract Fracpack is the hydraulic fracturing of high permeability (generally > 10 md) formations to increase well productivity and control sand production. Fracturing aspects of the fracpack process have been discussed recently in the literature.1,2 However, the reservoir engineering aspects and justification for fracpack have not been extensively studied. The reservoir engineering aspects of fracturing low permeability formations have been widely documented throughout the petroleum literature.3 However, fracturing high permeability formations differs from fracturing low permeability formations. To ensure the success of a fracpack treatment, the candidate well needs to be chosen carefully with consideration given to rock mechanics, reservoir engineering and operational aspects of the fracpack process. Generally, hydraulic fracturing is usually thought of as a technique to increase productivity or establish production in low permeability reservoirs. However, benefits can be realized by fracturing highly permeable formations that have formation damage and/or sand production tendencies. A well that has reduced permeability several feet or tens of feet away from the wellbore can be made more productive by fracturing through this damaged zone to contact undamaged reservoir. Reservoir fluids are thus provided an unrestricted pathway from undamaged reservoir to the wellbore. The conductivity within the fracture can be maximized so that pressure drop along the fracture itself can be held to a minimum. In the case of a well with sand production tendencies, a hydraulic fracture decreases the pressure drop necessary to produce the well at a given rate and changes the flow regime around the well such that sand production is minimized or eliminated. Thus the well may be produced at a rate higher than the unfractured critical sand producing rate. Operationally, fracturing high permeability formations is different from fracturing low permeability formations due to the expected high leak-off rate, which influences fracturing pressure as a function of time. In addition, because of the desired high fracture conductivity, the concept of tip screen-out is applied. In tip screen-out, the fracture is designed in such a way that by the time the fracture reaches the desired length, the leading pad volume has leaked off into the formation. After the pad volume has leaked off, the presence of the proppant-laden-fluid at the leading edge of the fracture initiates the screen-out process. Continued injection of the proppant laden fluid causes the fracture to widen or balloon, reaching a greater than average width and high proppant concentration (a packed fracture). During the packing period, the fracturing pressure is expected to sharply increase.