Data taken from a steady-state electrolytic model have been used to developcurves showing production increase as a f unction of fracture height, fracture length, reservoir height, drainage radius, fracture flow capacity, formation permeability and wellbore radius. The work allows a fullerevaluation of the effect of fracturing parameters on productivityincrease. Introduction Hydraulic fracturing methods for productionstimulation have become a common procedure in the oiland gas industry. Fracturing treatments areperformed on wells of various potentials to help increasethe production rate. In addition to the desire forincreased production is the need to predict whatincrease might be expected. This knowledge is usefulin economical treatment planning to accomplish thedesired production goals for the well. Theoretical production increases due to horizontalradial fractures may be calculated using equationsdeveloped from mathematical analyses and electricalmodels. It also is possible to predict theoreticalproduction increases due to vertical fractures usingcurves developed from electrical and mathematicalmodels." However, these studies assumed that thevertical fracture height and the formation height wereequal, which may not be true." In addition, the finalfracture height through which fluid is produced maynot be equal to the created height. The development of vertical fracture proppanttransport relationships has made unrealistic theassumption that propped fracture height is equal tocreated fracture height. Through the use of publishedproppant transport equations, it is possible tocalculate the height of a bed of propping agent depositedin a fracture of a given height. Assuming that thefluid flowing in the fracture moves through only thepropped portion of that fracture (i.e., that theunpropped part of the fracture heals) it becomesessential to know how production increase varies with theratio of propped fracture height to formation height. It should be recognized that future investigationmay determine that the fracture does not healcompletely and that a highly permeable channel existsover the deposited bed of proppant. The effect of thischannel was not considered for the present study. The following analysis of experimental dataallowed development of curves to determinetheoretical production increases considering fracture heightas a variable. Discussion In designing a fracturing stimulation treatment anumber of variables must be considered. The size ofthe treatment, type of proppant used, proppantconcentration, treatment fluid properties and wellconditions are all factors affecting the dimensions andpermeability of the fracture. Production increase due to a vertical fracture isaffected by propped length, height, width andpermeability of the fracture for a given set of formationconditions. Production increase may be defined asthe ratio of production rate after fracturing to theproduction rate before fracturing at the samepressure differential, pe - pw. JPT P. 633ˆ
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn 1996, the Gas Research Institute (GRI) performed a scoping study to investigate the potential for natural gas production enhancement via restimulation in the United States (lower-48 onshore). The results indicated that the potential was substantial (over a Tcf in five years), particularly in tight sand formations of the Rocky Mountain, Mid-Continent and South Texas regions.However, it was also determined that industry's current experience with restimulation is mixed, and that considerable effort is required in candidate selection, problem diagnosis, and treatment selection/design/ implementation for a restimulation program to be successful. Given a general lack of both specialized (restimulation) technology and "spare" engineering manpower to focus on restimulation, GRI initiated a subsequent R&D project in 1998 with several objectives. Those objectives are to 1) develop efficient, cost-effective, reliable methodologies to identify wells with high restimulation potential, 2) identify and classify various mechanisms leading to well underperformance, 3) develop and test non-fracturing restimulation techniques tailored to selected causes of well underperformance and, 4) demonstrate that, with improved technologies in these key areas, restimulation is a viable and attractive approach to improve well recoveries and economics.The approach adopted for the R&D program is a combination of candidate selection methodology development, conceptual well underperformance/problem classification, laboratory studies, and actual field experiments and demonstrations of restimulation treatments. At this time, a multi-process candidate selection methodology has been developed, consisting of production comparisons, engineering based performance assessments, and pattern recognition technology. Also incorporated into the overall methodology are individual well reviews, economic analysis, and a new short-term field test for candidate verification. Laboratory studies have also identified new procedures for effective clean-up of unbroken gel in propped and natural fractures.In total, twenty actual restimulation treatments are planned at four separate test sites. Currently active sites are in the Rocky Mountain and Mid-Continent regions. One site is located in the Big-Piney/LaBarge Producing Complex in the northern Moxa Arch area of the Green River Basin. As of this writing, three restimulation treatments have been performed at this location.The second site is the combined Rulison, Parachute and Grand Valley fields in the Piceance Basin. Candidate selection has been completed, and actual field-testing and restimulation activities are expected to begin in July 1999. The third site is the Carthage field in East Texas. Candidate selections are complete at this site also, with field activities also scheduled to begin in July. The fourth test site, not yet active, is in the Wilcox Lobo Trend of South Texas. This paper is the first comprehensive publication of results from this recent GRI init...
No abstract
In 1996, the Gas Research Institute (GRI) performed a scoping study to investigate the potential for natural gas production enhancement via restimulation in the United States. The results indicated that the potential was substantial, particularly in the tight sands of the Rocky Mountain, Mid-Continent and South Texas regions. However it was also determined that industry's historical experience with restimulation is mixed, and that considerable effort is required in candidate selection, problem diagnosis, and treatment selection/design/implementation for a restimulation program to be successful. As a result GRI initiated a subsequent two-year R & D project with the objectives: 1) to develop efficient, cost-effective, and reliable methodologies to identify wells with restimulation potential, 2) to identify and classify various mechanisms leading to well underperformance, and 3) to develop and test various restimulation techniques tailored to different causes of well underperformance. The approach adopted for the R&D program is a combination of conceptual methodology development, laboratory studies, and actual field testing of restimulation treatments in tight gas sand reservoirs. In total, four test sites are planned for the project; each site consists of about 300 total wells in a contiguous area and completed in a consistent producing horizon, out of which five are selected for actual restimulation. The first two sites are in the Rocky Mountain region, the first being in the Big-Piney/LaBarge Producing Complex of the northern Moxa Arch in the Green River Basin (Frontier Formation), and the second being the combined Rulison, Parachute and Grand Valley fields of the eastern Piceance Basin (Williams Fork Formation). At present, restimulation candidates have been selected, verification testing completed, and two restimulations performed at the first site; preliminary candidate selections have been made at the second site. The results to date from this project show why methodologies to accurately select "high - potential" restimulation candidates have eluded previous investigators. Each of the analytic procedures utilized thus far in the project is providing a different list of candidates, each based upon different criteria and with uncertainty as to the validity (or lack thereof) of each. While the situations being addressed in this project are understandably complex, specifically multilayered, heterogeneous reservoirs that are completed and stimulated in a wide variety of ways, the project experience to date supports that no acceptable methodology currently exists to universally select restimulation candidates across different geologic settings (which is the objective of this project). What is clear is that restimulation potential does appear to exist, as evidenced from the restimulation treatments performed to-date, but that some degree of site-specific knowledge and methodology customization is required. This is supported by the findings from the individual well reviews and laboratory studies. Clearly, more results from this project are needed to better understand the methodologies being investigated, and how they should be integrated to develop the efficient yet robust methodology sought.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOver the past 18 months the Gas Research Institute has initiated a restimulation study in wells in the Green River Basin, Piceance Basin and East Texas Cotton Valley Reservoirs. 1 New specific diagnostic procedures have been utilized to select candidates as well as intensive laboratory studies have been conducted to select specific candidates for restimulation. This paper will report on the laboratory testing, which involved fluidizing beds of proppant from previous treatments and also report results of effects of various chemicals on specific reservoirs.Several restimulation candidates case histories will be presented and a great deal of detail will be given in reference to refrac design, type of treatment and diagnostics utilized to ascertain success or failure of the treatments as well as production data. The program has illustrated that there are available diverting techniques that can function over long sections and achieve excellent stimulation. The authors will discuss laboratory testing procedures and specific recommendations in reference to selection of candidates and specific stimulation procedures that can be followed in various reservoirs.
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