Field Studies of Drilling and Completion Fluids to Minimize Damage and Enhance Gas Production in Unconventional Reservoirs

Abstract

Abstract Field data and lab data are presented for various fluids pumped in low perm shales, coalbed methane and tight sandstone reservoirs. Commonly used surfactants, alcohols as well as a microemulsion system (ME) are evaluated. Lab data is presented that illustrates the cleanup of injected fluids in tight gas cores. Damage mechanisms are shown to be phase trapping and high capillary pressures. The microemulsion additive results in lower pressures to displace injected fluids from low permeability core samples over conventional surfactant and methanol treatments. The observed enhanced relative permeability mechanism is the alteration of the rock-fluid interfacial tension or contact angle. It is demonstrated that this alteration effectively lowers the capillary pressure and capillary end effect associated with wellbores and fractures in low perm reservoirs by as much as 50%, thus mitigating phase trapping and therefore permitting an increased flow area to the wellbore following drilling and hydraulic fracturing. Over 300 wells were evaluated that were drilled and/or fracture treated with various fluid combinations in the Barnett, Fayetteville and Appalachian basin shales. Some 200 wells are examined in the San Juan Basin and other low perm areas such as the Pieance Basin, Uinta, Vicksburg and Cotton Valley. Drilling examples are shown for several horizontal wells. The addition of the microemulsion to fracturing treatments has resulted in more than 50 to 100% increases in load recoveries and gas production. Production analysis of horizontal wells drilled and cleaned up with the microemulsion shows a doubling of production over offsets. Pressure analysis of fractured wells shows that the damage factor is reduced by a factor of 2 with the inclusion of ME. This is a result of a combination of reduced depth of invasion, a higher relative perm in the invaded zone and/or longer effective frac lengths. Introduction The primary objectives of this study include:Examine factors that govern the cleanup of injected drilling and fracturing fluids.Present Case studies in several unconventional reservoirs comparing various surfactants in drilling and fracturing treatments looking at water recovery and oil and gas production. Commonly used fluids in unconventional resources are water with friction reducer and surfactant typically to lower surface tension. There are several factors that govern cleanup of hydraulic fractures. In addition to simple air-water surface tension, a factor that is typically overlooked is the interfacial tension between the rock and the injected fluid which is of prime importance in dictating capillary pressure and capillary end effects in gas wells. This becomes important available pressure does not overcome the capillary end effect leaving fluid trapped in the reservoir in a manner illustrated in Figure 11.