The performance of multiple hydraulic fracturing treatments along a 2000-foot horizontal well bore was completed in a gas bearing, naturally-fractured shale gas reservoir in Wayne County, West Virginia. Pre-frac flow and pressure data, hydraulic fracturing treatments, and post-stimulation flow and pressure data form the basis from which a comprehensive analysis was performed. Average field production from 72 wells was used as baseline data for the analysis. Such data was used to show the significance of enhanced production from a horizontal well in a field that was partially depleted. The post-frac stabilized flow rate was 95,000 cubic feet per day (mcf/d) from 2000 feet of horizontal borehole. Under current reservoir pressure conditions, the horizontal well produced at a rate 7 times greater than the field current average of 13 mcfd for stimulated vertical wells. This increase in gas production suggests that horizontal wells, in strategically placed locations within partially depleted fields, could significantly increase reserves.
This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract One- and two-dimensional gas reservoir simulators were combined in such a manner that pressure distributions, both in an induced pressure distributions, both in an induced vertical fracture and in the surrounding formation, could be determined as a function of time for any specified well production rate. Basic assumptions regarding the fracture were as follows:the fracture completely penetrates the formation,all flow into the wellbore enters via the fracture, andflow in the fracture is described by Darcy's law. The technique used consisted basically of the alternate use of one- and two-dimensional algorithms for obtaining new pressure distributions in the fracture and the reservoir, respectively. The finite-difference grid penetrates the fracture in the direction normal penetrates the fracture in the direction normal to the fracture axis so that corresponding to each fracture node, there is an adjacent reservoir node. The pressures at these adjacent nodes were used to calculate flow rates from the formation into the fracture, which provided source terms for both algorithms. By alternately using large and small timesteps, stabilized distributions were obtained after a few days production for several different fracture permeabilities. All other reservoir and fracture parameters were fixed so that the effect of fracture permeability on fracture pressure drop and well pressure decline could pressure drop and well pressure decline could be determined. Results are presented for a production rate of 1 MMscf/day from a 40-acre production rate of 1 MMscf/day from a 40-acre square of 2 md-ft flow capacity. The combination model developed provides the only known means of simulating a vertical fracture of given characteristics in a gas reservoir under transient conditions. Thus, the technique developed would be useful in locating wells in a storage field in that the effects of both fracture length and conductivity could be considered prior to drilling and fracturing operations. Introduction The American Gas Association Pipeline Research Committee and the U.S. Bureau of Mines are involved in a cooperative study of methods for increasing the capacity and operating efficiency of gas-storage reservoirs. The expansion of an existing storage field to achieve increased capacity frequently requires that new wells be drilled and fractured. The question thus arises: With regard to the area's preferred direction of fracture and the preferred direction of fracture and the existing formation permeability, what is the minimum number and location of new, fractured wells required to achieve the desired increase in capacity?
This paper discusses drilling a 2,000-foot horizontal well in the Devonian Shale, Wayne County, West Virginia, to test the concept that multiple hydraulic fractures from a horizontal wellbore can increase gas recovery efficiency over vertical stimulated boreholes. Discussion focuses on the air/mist drilling, wireline probes, and bottomhole assemblies that were used to drill the well, The target was a 50-foot zone located at a depth of 3,400 feet. Total hole length was 6,020 feet. The angle-building section was achieved using a 4.25 degrees/100-foot design to reduce the risks associated with casing installation in the horizontal section. Directional control methods proved to be unreliable in an air-drilling environment. Bottomhole assembly performance was heavily dependent on motor life and lithologic type. The completion program for the well consisted of installation of 4 1/2-inch casing with external casing packers and port collars. This completion string was installed in 2,000 feet of open hole section that was air drilled. Both geophysical well logs and a borehole television camera survey were used to design the casing string so that shale intervals could be isolated for testing and evaluation before and after stimulation. Background The drilling of directional wells and even horizontal wells to augment oil and gas production goes back to at least 1944 in the Appalachian Basin wherein a horizontal well was drilled from a 500-foot deep shaft in the Franklin Heavy Oil Field in Venango County, Pennsylvania, to improve oil recovery. Several hundred feet of horizontal core was taken during the drilling operations in the Venango Sand to characterize the reservoir. The Federal Government has been investigating the application of high-angle drilling to improve reservoir access in tight formations for more than 20 years. The focus of much of this research was to determine the properties of earth fracture systems in productive Devonian shale reservoirs and to develop improved techniques for recovering hydrocarbons with increased efficiency. The value of high-angle drilling perpendicular to natural fracture systems for maximizing production from fractured reservoirs was recognized early. Several field tests have been conducted to investigate the concept. In 1972, a high-angle borehole was drilled in Mingo County, West Virginia, to a measured depth of 4,678 feet with an average deviation of 41" from vertical through the Devonian shale section. After establishing the feasibility of drilling high-angle wellbore using air, a subsequent well was drilled to 53 degrees in the Cottageville Field, Jackson County, West Virginia. Total measured depth of that well was 4,736 feet. Experience from these two directional wells using mud motors on air identified many limitations of economic directional drilling. In DOE's latest experience, an oriented core was obtained from a Meigs County, Ohio, Devonian shale directional well to determine natural fracture spacings. High-angle air-drilling experience using downhole motors is not well documented in the petroleum literature. The most recent experience in air-drilled high-angle wells is the Grand Canyon Directional Drilling and Waterline Project which was accomplished using air-driven motors and wireline steering probes. Conventional wellbore sizes and tools were used to achieve a 71 degrees hole angle. Recent reservoir modelling studies used to estimate recovery efficiency of a Devonian shale horizontal well show a two- to three-fold increase in gas reserves per unit volume of reservoir. P. 291
A series of stimulations were designed to open and propagate natural fractures known to exist along a 2000 foot horizontal well in Wayne County, West Virginia. The stimulations were also designed to induce fractures in the formation as well as propagate the natural fractures by manipulating pressure and injection rates. A number of radioactive tracers were used to determine where fractures were opened and propagated at different injection rates. The tracers were found in fractures in zones other than the one pumped into, a fact considered prima facie evidence that natural fractures with two or more orientations had been opened and propagated. Pressure testing and gas sampling of the isolated zones confirm that fracture communication was accomplished along nearly 1000 feet of borehole by stimulation of one 400 foot long section. A technique for inducing multiple hydraulic fractures with multiple orientations was demonstrated. Background Horizontal wells are drilled to solve production problems or to improve hydrocarbon production problems or to improve hydrocarbon recovery efficiency from a particular reservoir. It is believed that the original concept of drilling horizontal wells was to contact more formation in a reservoir which was not a particularly outstanding producer, or which had other production problems. One of the earliest known attempts problems. One of the earliest known attempts at horizontal drillin in th United States was that done in the Venango sandstone from a shaft drilled near Franklin, Pennsylvania in 1944. The particular problem being addressed was how to produce the heavy crude oil which had lost its solution gas because of the shallow depth of the formation (less than 50 feet) and thus was produced at slow rates. Later efforts addressed themselves to tight, low permeability shales and sandstones which were productive only as a function of the natural productive only as a function of the natural fractures which are conduits for the reservoir hydrocarbons. The ideal wa to improve recovery efficiency is to increase the total number of natural fractures which can be connected to a single wellbore for drainage. Thus the concept of drilling a well in a particular direction and attaining an inclined angle (40 to 90 degrees) was a logical means of improving upon the recovery efficiency of a vertical wellbore. A method of improving the gas recovery efficienc of inclined of horizontal wellbore in a naturally fractured reservoir is to extend the geometry and flow capacity of existing fractures as well as create new induced hydraulic fractures. This can best be accomplished by stimulating the natural fractures which exist in the reservoir by inflating them with a non-damagin fluid and propping the inflated fractures to maintain the propping the inflated fractures to maintain the enhanced flow capacity and to induce additional fractures by increasing the injection rate. This was the technical approach used to stimulate gas recovery from the Devonian shales in the horizontal well. This type of operation can be accomplished quite readily if the right geologic condition can be found. That condition is generally associated with normal or block faulted areas where multiple fracture directions are generated in association with the faulting. Other conditions where multiple fracture sets are generated are associated with thrust faulted areas. Several geologic settings were selected in Wayne and Lincoln Counties, West Virginia, which were known to have multiple fracture sets as a function of the pre-Cambrian rift-type basement faulting which produced the Rome Trough, and the test well was drilled in one of them. P. 27
This report presents a summary of the geologic site selection studies, planning, drilling, completing, stimulating, and testing of two horizontal wells drilled in the Devonian Shales of the Appalachian Basin in West Virginia. Each horizontal well was designed and managed by BDM as the prime contractor to the Department of Energy. The first well was drilled with industry partner Cabot Oil and Gas Corporation in Putnam County, West Virginia. The second well was drilled with Consolidated Natural Gas Company in Calhoun County, West Virginia. This report summarizes four reports prepared by BDM which detail the site selection rationale and the drilling and completion operations of each weil. Each horizontal well is currently producing commercial quantities of hydrocarbons. The successful application of horizontal well technology represent continued development of the technology for application to tight and unconventional natural gas resources of the United States. Continued technology development is expected to ultimately result in commercial horizontal well drilling activity by industry in the Appalachian Basin. ix 1.0 EXECUTIVESUMMARY This report summarizes the geologic studies, site selection, drilling, logging, completion, and well _testing of two horizontal wells t drilled in the gas-bearing Devonian Shale interval in the Appalachian Basin. Detailed technical information concerning each of the two wells reviewed in this volume will be found in the technical report for each weil. Cash flow analyses were undertaken for each horizontal well using the well-specific cost and production information available through the end of January 1992. These results, detailed in this volume, show that a horizontal well is economic over a wide range of economic conditions if: (1) The well cost can be controlled to between $500,000 and $700,000 and (2) If the well is likely to produce at least 140 Mcf/day over the first year of operations, depending on the price of natural gas.
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