Conglomerate Reservoir Research Articles

A New Development in Completion Methods- The Limited Entry Technique

Abstract Shell Oil Co., in Texas and New Mexico, has experienced excellent results from an improved well stimulation method called the limited entry technique. This method has proven much more effective than any other method in treating thick pay sections and in diverting treating fluids to multiple horizons. The limited entry treatment technique is accomplished bylimiting the number of perforations in a well andproviding sufficient injection rate to require the restricted flow capacity of the perforations to divert the treatment to a greater portion of the perforated interval. From Dec. 3, 1960, to Jan. 1, 1963, Shell Oil Co. in Texas and New Mexico has treated 363 wells by this technique. The production performance of wells treated by limited entry completions is superior to that of conventionally treated wells. Gamma-ray tracer logs indicate most of the pay is being treated even though not covered by perforations. The limited entry technique has been used successfully in treating two separate reservoirs simultaneously in dually completed wells. Results of these simultaneous treatments have been gratifying in both well performance and reduced costs. Introduction The efficient simultaneous treatment of multiple porous intervals in a reservoir has been a long-standing problem in well stimulation. Various methods have been used to treat multiple zones with greater or lesser degrees of effectiveness. The bridge plug and packer method is effective, but is relatively expensive. Further, the injection rates are considerably reduced, and it is sometimes mechanically hazardous. Temporary plugging agents to divert the treatment have been used with apparent success. The main disadvantage of temporary plugging agents such as moth balls or gel blocks is the difficulty in determining the proper quantity of agent required to divert the treatment. Ball sealers are often ineffective because offluid communicating behind the casing between closely spaced perforations,failure of the ball sealers to seat on the perforations andabrasion of the ball sealers allowing fluid to by-pass. These stimulation techniques (for the purposes of this paper) are considered to be conventional treatment methods. The basic objective of all stimulation efforts is to make the best well, compatible with cost. To get an effective treatment, it is desirable to treat as much of the perforated interval as possible. Also, the treatment should be proportioned into the perforated intervals. Well performance has proven that both of these objectives can be better fulfilled by a properly designed limited entry treatment, than by conventional treatments. Limited Entry Technique Shell Oil Co., in Texas and New Mexico, has experienced excellent results from an improved well stimulation method called the limited entry technique. Based upon data obtained to date, this method is far superior to the other methods of obtaining simultaneous treatment of multiple zones or thick pay sections. The treatment is performed bylimiting the number of perforations in a well andproviding sufficient injection rate to require the restricted capacity of the perforations to divert the treatment to a greater portion of the perforated interval. The first limited entry treatment in this region wad performed in Shell TXL M-3, TXL Tubb field, Ector County, Tex., following a review of a paper by Murphy and Juch of Compania Shell de Venezuela. From Dec. 3, 1960, to Jan. 1, 1963, 363 limited entry treatments have been performed in many different reservoirs (see Fig. 1). No mechanical difficulties have been encountered that can be attributed to this method of treatment. Treatment failures due to "sand-outs" have not been increased by this method. Treatments have been successfully performed in carbonate, sandstone, conglomerate and chert reservoirs. These reservoirs range in depths from 3,100 to 9,500 ft. with bottom-hole pressures varying from 1,000 to 3,600 psi. Basic Theory of Fracturing Process Conventional Treatment The simultaneous treatment of multiple porous intervals by conventional methods is depicted in Fig. 2. JPT P. 695^

Contained Injection Pattern and High Pumping Rates Solve Permeability Problems in a North Texas Caddo Conglomerate Water Flood

Abstract To effect any successful waterflood operation, it is essential to first recognize the problems to be confronted and then to properly apply basic techniques to solve them. In the case of the Rusmag field the major problem was the highly varying permeability profile native to the Caddo conglomerate reservoir. The operator has apparently controlled this problem, as evidenced by 2.5 years of successful performance under waterflood operations. Although there currently are four separate flood efforts being conducted in the Rusmag field, this paper is concerned chiefly with presenting a case history of the Rusmag Unit waterflood. The Unit contains the major portion of the reservoir, and 2,500 of the approximately 4,000 acres in it currently under flood, with the remaining acreage scheduled for development in 1962. Unit oil production is near 2,000 B/D, with water-injection rates averaging 400 B/D at pressures ranging from 0 to 550 psi. Cumulative waterflood oil recovery to Jan. 1, 1962, has been 573,765 bbl, with an ultimate recovery of 2 million bbl of oil possible. JPT P. 1104^

Tippett Field, Crockett and Pecos Counties, Texas

The Tippett field comprises a group of eight pools located in northwestern Crockett County and adjacent Pecos County, Texas. The field was discovered in 1947, and to January 1, 1960, has produced about 2,700,000 barrels of oil and 1,540 million cubic feet of gas. The chief producing zones are conglomerates in the basal Permian at 5,800-6,300 feet. Minor producing zones are found in middle Permian dolomite from 3,800 to 4,500 feet. The trap is formed by an anticline about 6 miles long and 4 miles wide, the axis of which trends northwest and southeast. The structural relief on the basal Permian pay zones is about 300 feet. The anticline is clearly discernible at the surface, so that discovery may be credited to both surface work and shallow stratigraphic drilling. Total pro uctive area is about 2,540 acres. Though water is found in the basal Permian conglomerate reservoirs, a large gas cap in most of them probably furnishes most of the oil-producing energy. Some conglomerate reservoirs contain only gas. The pay conglomerates appear to be derived from Devonian and Ordovician cherty limestones and dolomites, which were truncated by Pennsylvanian erosion. The residual cherts seem to have been reworked into shingle beaches and then consolidated into porous conglomerates containing very little calcareous cement. Future productive prospects lie chiefly in gas reservoirs on the structurally higher part of the anticline.

Oil and Gas Geology of North-Central Texas: ABSTRACT

In this area of more than 42,800 square miles more than 2,615,653,966 barrels of oil have been produced from Paleozoic rocks. Sandstone, conglomerate, and carbonate reservoirs have oil and gas accumulations in both stratigraphic and structural traps. Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian rocks reaching a total maximum thickness of about 19,000 feet prevail in the area. Pennsylvanian and Permian strata contain remarkable carbonate reefs of various kinds which if completely encased in shale form excellent oil and gas traps. Major structural features include the Bend arch, Electra arch, Muenster arch, Fort Worth basin, Baylor basin, Fort Chadburne fault zone, Concho arch, and End_Page 123------------------------------ the buried Ouachita Mountain overthrust belt. Gently dipping surface strata of Permian, Pennsylvanian, and Cretaceous rocks mask most of the deep subsurface structure. End_of_Article - Last_Page 124------------

Geology of Elk City Field: ABSTRACT

The Elk City field is in T. 10 N., R. 20-21 W., Washita and Beckham counties, Oklahoma, on the north front of the Wichita Mountains near the axis of the Anadarko basin. The field was discovered by the Shell Oil Company's J. G. Walters well No. 1 in the NE. ¼, SW.¼ of Sec. 14, T. 10 N., R. 21 W., which was completed in November, 1947, from a reservoir at the depth of 9,260-9,360 feet with an initial daily production of 470 barrels, 65.4° A.P.I. gravity condensate, 25 barrels fresh water, and 5,650 MCF of gas. Crude oil was discovered and first produced by the field's second well, the Shell-Long No. 1, NE. ¼, SW. ¼ of Sec. 15, T. 10 N., R. 21 W., which was completed in February, 1949, from a reservoir at a depth of 9,040-9,080 feet, with initial production of 2,345 barrels, 49.1° A.P.I. gravity crude oil, 70 barrels of fresh water, and 3,661 MCF of gas. Subsequently, development has proved several reservoirs in the Missouri series of the Pennsylvanian to be productive of condensate and oil at a depth range from 8,800 to 10,200 feet. The field has a productive extent at present of 7 miles in length and 2 miles in width as determined by about 30 wells producing condensate and crude oil. The probable productive limits have not been indicated along the axis of the field but two dry holes on the north and south flanks, respectively, restrict the probable productive width to less than 3 miles. In the Missouri series of the Pennsylvanian system, this field is structurally an elongate anticline with about 400 feet of closure trending west-northwestward with several culminations along the axis. The initial folding of this structure is unknown due to inadequate knowledge of the deeper strata, but drilling to date has proved that the structure was present during post-Missouri pre-Virgil time. This is shown by angularity at the base of the Virgil series. Further folding probably occurred in Upper Pennsylvanian, Permian, and post-Permian time. The surface beds are Permian in age and extend to a depth of about 6,500 feet. The Pennsylvanian system is composed of more than 7,500 feet of strata extending from 6,500 to below 14,000 feet. The deepest well drilled is the Continental's Proctor No. 1, in the center, NW. ¼ of Sec. 28, T. 10 N., R. 20 W., which penetrated the Pennsylvanian to the depth of 14,572 feet. Although oil and gas showings have been encountered both above and below the Missouri series, the field is presently being exploited from the granite wash and conglomerate reservoirs from 8,800 to 10,200 feet. These reservoir strata are interbedded with shale and marine limestone, but the series is predominantly of a coarse clastic type which ranges lithologically from heterogeneous granite wash to pure quartz sandstone and to limestone conglomerate. Most conceivable combinations of clastic material are present to some degree. One of the more reliable structure markers is a limestone at the top of the Kansas City group located about 500 feet below the top of the Missouri series at a depth of about 8,700 feet. This limestone formation is readily identified from electric logs and is commonly used as a datum for structural interpretation since it immediately overlies the first productive reservoir of the field. Some of the characteristics of the producing reservoirs have been established but more extensive development is necessary to define the total number of reservoirs and their productive extent. All data however show that this is a major field and of importance to the future development of the vast Anadarko basin. Oil and gas recoveries in this field justify the deep drilling necessary and the further exploration for similar accumulations. End_of_Article - Last_Page 626------------