Key Production Co. began using short-radius, moderate length openhole horizontal lateral recompletions in re-entries of wells in a limestone/dolomite reservoir in northwest Texas. They found that a few wells needed some type of stimulation to achieve optimum production rates. A dual lateral (90° opposed) was drilled on one re-entry to improve production performance. This well was in an area of the field with below-average reservoir quality, and production rates were still disappointing even with two lateral sections. Fracture acidizing was the most likely method to achieve the degree of stimulation needed. There was concern that this might lead to unwanted communication with the aquifer zone below the oil column. Conventional stimulation methods could not achieve multiple, well-spaced, limited-sized fractures.
The operator used a new hydrajet-fracturing technology that has shown a very high success rate in other areas to achieve the stimulation needed for this well, and at acceptable cost. Six separate fractures were placed at selected locations along each of the two lateral sections (12 distinct fractures) in less than 8 hours from first pumping to final displacement. The resulting production rates far exceeded the operator's expectations. This paper presents a brief review of the hydrajet-fracturing stimulation process and specific details related to its highly successful application in this Level 1 dual-lateral completion.
In 1998, Key Production Co. acquired the production and drilling rights to several leases in Hardeman County, Texas (Fig. 1). Of specific interest is production from the Meramec and the Chappel formations. In this region, the Meramec is primarily a limestone formation, and the Chappel is a moderate- to low-permeability limestone/dolomite reservoir that produces oil from approximately 7,800 to 8,200 ft and overlies the Ellenberger Aquifer. Typically, where the Chappel has been more completely dolomitized, there is better permeability and porosity, yielding higher production rates.
Primarily, conventional vertical well completions have been employed throughout this field. Two of the more common completion methods used are represented inFigs. 2 and 3. Both of these completion plans drilled a 12 1/4-in. hole to approximately 500 ft and cemented in 8 5/8-in. surface pipe. As shown in Fig. 2, some wells were then drilled into the Chappel formation until porosity was found. If a drill stem test (DST) indicated oil was present, the 5 1/2-in. casing was run with a formation packer shoe on bottom. The packer shoe was set in the tight lime above the porosity and the casing was cemented. The shoe was drilled out and the well completed opehnole, typically without any type of stimulation treatment. Another common completion method used (Fig. 3) continued drilling into the primary-hole well into the Chappel lime 100 to 400 ft, depending on the local geology of the reservoir. The 5.5-in. casing was run to total depth (TD) and cemented back to 500 feet above the Meramec. These wells were completed by perforating and, if required, acid stimulated.
From the early to mid-1980s, some wellbores were plugged and abandoned as dry holes with no casing being set. After studying the geology of the reservoir, Key Production Co. believed that some of these locations could be re-entered and economic production rates achieved using short-radius, moderate-length, openhole horizontal laterals. Fig. 4 is a schematic representing one of the abandoned wellbores recompleted as a horizontal well. In a part of the field considered low-quality, the operator decided to recomplete one of the abandoned wellbores in the Chappel lime as a Level 1 dual-lateral completion, with the laterals at similar depths and opposed by 90° (Fig. 5). The laterals were approximately 780 and 800 ft in length. After completing the second lateral and swabbing/flow-testing the well for two weeks, the team decided that some form of production enhancement treatment was needed to achieve optimum production rates.