Success Achieved in Lenticular Reservoirs Through Enhanced Viscosity, Increased Sand Volume, and Minimization of Echelon Fractures

Abstract

A common trend in our industry is to minimize gel concentrations and utilize the lowest viscosity fluid available to place proppant Barrett Resources Corporation has found, for lenticular microdarcy formations, that one of the keys for success is enhanced proppant transport. This is achieved incorporating stable gels which maintain greater than 1000 cpa viscosity at bottomhole static temperature for the duration of the treatment. An extensive case study has been completed, involving over 500 fracture stimulation treatments in more than 175 wells, that illustrates the poor results achieved in the Williams Formation of the Mesaverde Group using low viscosity fluids. Low viscosity fluids invariably exhibit poor proppent transport. The statistical study shows that larger treatments utilizing "perfect proppant transport" fluids gain superior results. Based upon the case study, 100% economic success has been achieved upon incorporating stable fluids containing delayed breakers, reducing ped volumes to less than 5% of total job size, and minimizing echelon fractures while implementing a limited entry stimulation technique. Background Barrett Resources Corporation has drilled and completed over 175 Williams Fork producers across the Grand Valley, Parachute and Rulison Fields within the Piceance Basin of Western Colorado (Figure 1). The Williams Fork Formation lies within the upper portion of the Cretaceous Mesaverde Group and is the primary target for development in the area. Depths range from 5900 to 8300 feet. Each well must be fracture stimulated to yield commercial production through a series of limited entry treatments ranging from one treatment to as many as six fracture stimulations to complete the entire gas saturated section. An interval from 100 to 600 feet in gross thickness may be considered for an individual treatment. Limited entry techniques must be employed to stimulate the numerous and discontinuous lenticular bodies or point bars within a selected interval. Evaluating the success of previous stimulations to optimize future treatments caused Barrett to embark upon a large statistical study of our completion practices. Prior to the study, Barrett essentially perforated most mud log shows in attempting to recover gas from the numerous lenticular sands present in each well. A typical perforating scheme would include 20 to 30 holes distributed between 5 to 10 sand bodies within a zonal treatment. Stimulations ranged from 100,000 lbs. of sand to 350,000 lbs., incorporating through time, virtually every water based fluid available. As a result, a statistical analysis of the previous treatments produced a number of meaningful conclusions enabling Barrett to improve gas recovery while reducing overall well cost. Geology The gas saturated portion of the Williams Fork Formation is 1700 to 2400 feat in thickness and encompasses all of the peludal interval (commonly referred to as the Cameo), the coastal, and the majority of the fIuvial interval (Figure 2). The formation consists of interbedded silts, shales, and sands with numerous coals interspersed throughout the paludal (lower) section. All of the sands are fluvial in nature and are very heterogeneous and discontinuous. The two main fluvial (river) deposits are distributary channel sands and meanderbelt complex sands. P. 293

Case History: Observations From Diagnostic Injection Tests in Multiple Pay Sands of the Mamm Creek Field, Piceance Basin, Colorado

“…[1][2][3] Similar to Grand Valley, Parachute, and Rulison Fields, Mamm Creek Field production is principally from the Mesaverde Sands within the Williams Fork Formation. For a typical well within the Mamm Creek Field, the gross gassaturated interval is approximately 2,000-ft thick and consists of interbeddeded sandstones, siltstones, mudstones, shales, and coals.…”

“…Several authors [1][2][3][4] noted the importance of natural fractures to the productivity of Mesaverde sandstones. Perhaps the best example of the importance of natural fractures was demonstrated during the MWX project.…”