As the development of tight/unconventional and partially depleted gas reservoirs has increased, so has the demand for more innovative hydraulic fracture designs. Operators are increasingly placing proppant with slickwater, linear gel or hybrid fracture designs. While the benefits of these designs are typically attributed to a reduction in gel damage of the proppant pack, many operators mistakenly believe that the resulting fractures are not conductivity-limited.
Since few (if any) models on the market can adequately model the propagation of a slickwater frac as well as the associated proppant transport and deposition, it becomes difficult to optimize these fracture designs. This has led many operators to incorrectly assume that only small diameter sand or resin-coated sand may be placed in these types of designs, and that these products supply ample flow capacity.
However, one East Texas operator has combined insight into proppant transport with an appropriate understanding of realistic proppant pack conductivity to develop a novel, hybrid slickwater fracture design. This design has allowed the placement of larger diameter, higher conductivity proppant in fractures that many believed could not be placed either operationally or economically. Additionally, this operator has developed a unique pumping strategy to place the highest conductivity proppant in portions of the fracture where it provides the most value.
This paper will present a case history of these new hybrid slickwater fracture designs in this operator’s East Texas, Cotton Valley – Taylor completions. The design theory and sequential improvements will be documented, including larger diameter, higher strength proppants, as well as a novel placement design. Field results from the first six wells fractured will be presented, showing substantial increases in gas production compared to similar offset completions. Economics will also be shown to illustrate the tremendous value added to completions utilizing this hybrid fracture design.
The Cotton Valley Group was deposited during the Upper Jurassic Period and is predominately a deltaic dominated clastic unit. In Rusk County the Cotton Valley Group is approximately 1,500 ft thick. The basal portion of the Cotton Valley Group is called the Taylor Sand. It is bounded below by the Bossier Shale and above by a relatively tight carbonate unit referred to as the Taylor Lime. This carbonate unit also appears to provide separation from the more water-prone members in the Cotton Valley Group.
The Taylor Sand was deposited in a marine dominated deltaic environment. It consists of fine-grained sandstone and silts, which results in relatively low effective porosity. The average gross thickness of the Taylor Sand through the study area is about 250 ft. The porosity in the interval ranges from 7-14%, with an average value of 9%. Water saturation averages about 32% and is generally considered to be connate saturation. Permeability was not measured, but is believed to be in the range of 0.04 to 0.1 md in the study area.
The case study area is in the Minden Field just southwest of Henderson, Texas, in Rusk County. Wells have been drilled in the field since the late 1970’s to the present. The reservoir being studied specifically targets the Taylor Sand.
Author(s): Patrick Handren, SPE, SPE, Ascent Operating; and Terry Palisch, CARBO Ceramics
Paper Number: SPE 110451