CHAPTER 9 HAYNESVILLE (ARKANSAS PORTION)

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1 CHAPTER 9 HAYNESVILLE (ARKANSAS PORTION) Location About four-fifths of the Haynesville field lies in Louisiana and the remaining fifth in Arkansas, in T. 19 and 20 S., R. 20 W., Columbia County. The topography is gently rolling with elevations around 300 feet above sea level. History of Development The Haynesville field was discovered through the completion of T. L. James et al., Aiken No. 1, Claiborne Parish, Louisiana, November 25, 1941, in the Pettet limestone producing from 5,406 to 5,445 feet. The first well drilled in the Arkansas segment of the field, Navarro Oil Company, S. J. Beene No. 1, in fractional section 10, T. 20 S., R. 20 W., was completed December 15, 1942, at a total depth of 5,540 feet. The casing was perforated with 72 shots from 5,462 to 5,478 feet opposite the Pettet limestone of the Glen Rose formation (lower Cretaceous). Initial production was 92 barrels of 38.4 API gravity oil in two hours through a 3/8-inch tubing choke with a casing pressure of 1,000 psi, a tubing pressure of 250 psi, and a gasoil ratio o 400 cubic feet per barrel. Wells were drilled on an 80-acre spacing pattern. Early in 1946 the Arkansas segment of the field contained 33 wells, all producing from the Pettet limestone, a few from the lower porous portion of this zone but most of them from the upper porous part. Cumulative production for the Arkansas portion of the field up to the middle of 1946 totaled 1,670,246 barrels of oil and 2,728,901 Mcf of gas. Peak production was reached during May 1945, when the monthly yield was 71,316 barrels of oil and 128,892 Mef of gas. By December 1945, the output had dropped to 37,323 barrels of oil and 104,111 Mcf of gas for the month. The reservoir pressure which originally was 2,344 psi had dropped to 1,317 psi by December 1945, a decrease of 1,027 psi. As a result a pressure maintenance project was authorized by the Louisiana Department of Conservation April 24, 1944, and by the Arkansas Oil and Gas Commission April 26, 1944, and is underway. The operating interests of the Arkansas segment of the field as well as those in Louisiana have been unitized. Producing gas-oil ratios were low in the early life of the field, there being no gas-cap and only about 400 cubic feet of gas in solution per barrel of oil. The gas-oil ratio increased enormously from the original 400 cubic feet per barrel to 3,206 cubic feet per barrel in December 1945, and it was apparent that only maintenance of pressure could insure a reasonable recovery of oil from the reservoir. Geology Recent alluvial deposits and exposures of sands and clay of the Claiborne formation (Eocene) are found in the vicinity of the field. The stratigraphic section of this large oil field, p. 51, is generalized. Pettet limestone lentils which constitute the reservoir rock from which oil and gas are produced in the Haynesville field consist of coquina limestone containing a small percentage of normal oolites. All components of the limestone (large shell fragments, small fossils, and oolites) have been subjected to partial solution and much calcium carbonate has been reprecipitated both concentrically on the separate particles and in a fine granular condition in the interstitial spaces. A rock of relatively slight permeability and fair porosity has resulted. Coregraphs reveal large percentage differences in porosity and permeability in the producing zone. The accumulation of oil in the Pettet limestone is confined to two porous zones about 50 feet apart below 5,200 feet in depth. The uppermost is the main oil reservoir of the Arkansas portion of the field. Both zones are readily identified on electric logs that are available for all of the wells drilled. A structure map has been prepared with contours representing the top of the upper producing zone (Fig. 20). The total effective producing thickness of the Pettet lime is indicated on the map by isopach lines. The field as a whole lies on an elongated anticline trending east-west, the Arkansas segment being along the north flank. The nose of the fold plunges westward. The northern limit of production had not been reached by the wells which had been drilled up to the middle of The eastern and western limits in Arkansas' are determined by disappearance of porosity in the Pettet limestone of the Sligo formation in those directions. The field is, therefore, a combination structural and stratigraphic trap. Reservoir Data The oil produced in the extension of the Haynesville field in Arkansas averages 41 to 42 API in gravity. A typical sample had a gravity of 41.4 API ( sp. gr.) at 60 F. and a viscosity of 4.3 centipoises at

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3 100 F. The viscosity of the oil at original reservoir conditions of 2,344 psia and 179 F. and saturated with gas was 0.61 centipoise. However, as gas is released from solution at reservoir temperature by reduction of pressure to atmospheric, the viscosity increases to 1.7 centipoises (Fig. 21). The crude oil shrank 25 per cent in coming from original reservoir to atmospheric conditions of temperature and pressure owing to the loss of 514 standard cubic feet of gas per barrel of stock-tank oil which were in solution (Fig. 22). Hence the formation volume factor is The thermal expansion factor of the oil at 3,000 psi was volumes per volume per 100 F. increase in temperature and the compressibility of the oil saturated with gas at reservoir temperature is 1.5 X 10-6 volumes per volume per psi change in pressure. Both oil and gas are of good quality (Table 17). The gas is relatively rich in natural gasoline and nearly 50 per cent of the oil under reservoir conditions is composed of hydrocarbons simpler than heptane. At least a dozen coregraphs reveal large percentage differences in porosity and permeability in the producing zone. The highest porosity measured 29 per cent, the lowest 10 per cent. The highest permeability recorded is 316 millidarcys for one small piece of core,

4 the lowest average (for an edge well) is 1.8 millidarcys. The average of porosity measurements is 18 per cent and of permeability either 13.6 millidarcys or 42.2 millidarcys, depending on whether the one measurement of 316 millidarcys is discarded or included in the average. The average connate water saturation (determined from four wells) is 22.3 per cent. The salt water in the Pettet reservoir is highly saline (Table 18). Data from Figure 20 were used to determine that the bulk volume of the portion of the Haynesville reservoir which is in Arkansas is 32,220 acre-feet and the productive area in Arkansas is 3,426 acres. The productive zone is thin and averages only 9.4 feet in thickness. The reservoir had no gas-cap at discovery and consequently there were about 26,000,000 barrels of stock-tank oil in the reservoir north of the Louisiana- Arkansas boundary line when the pool was discovered. Secondary Recovery In spite of the fact that the original reservoir pressure was normal for the depth, no well has produced a significant amount of water and no indication of a natural water-drive has been observed. Reservoir pressures were lower on all sides of the field than in the center. Furthermore, reservoir pressure declined in proportion to withdrawal of fluid, pointing to a depletion-type reservoir. During the early life of the field gas-oil ratios were low but as the pressure of the reservoir declined and gas was released from solution in the oil, gas-oil ratios increased greatly

5 ( Fig. 23). Consequently, the force of gravity and the expansion of gas are the only forms of energy available naturally in the field to move oil to the wells. However, the permeability of the producing zone is so low that gravity drainage of oil into wells from the surrounding formation will be trivial. Calculations based upon the reservoir data show also that all the gas originally in the reservoir (in solution in the oil) will have been produced by the time the reservoir pressure has declined to about 300 psi and that under such conditions only a relatively small portion of the oil in place originally will have been produced. Consequently, in order to obtain maximum recovery of oil from this depletion-type reservoir of low permeability, maintenance. and restoration of energy would be required. Careful study of the reservoir data showed that the injection of gas into the reservoir was the most feasible method of supplying the energy required to increase the recovery of oil. The injection of gas was proposed by the operators in the field in 1944 and the project was authorized by the regulatory bodies of the states of Arkansas and Louisiana to maintain reservoir pressure and increase the recovery of oil. Not only would the recovery of oil from the field be increased, but also the gas and natural gasoline, which otherwise would have been vented to the air under normal operating practice, would be recovered in the gas-injection operations. All interests in the pool were unitized, a necessary procedure in insuring success for so difficult a problem as the Haynesville reservoir. The degree of success of the pressure maintenance operation will be determined by the ability of the operators to control the producing gas-oil ratios of wells. Adequate control of producing gas-oil ratios is accomplished only by complete freedom in the selection of injection and producing wells without the complication of individual ownership rights. Other important advantages such as elimination of many unnecessary tank batteries and lease lines and duplication of operating equipment of all kinds and material reduction of personnel required accrued to the operators through unitization. The average spacing of the oil wells in the field is about 87 acres and of injection wells 635 acres ( Fig. 20). About 15,000,000 standard cubic feet of gas per day can be returned to the reservoir. Careful study of the reservoir also has revealed the desirability of injecting water into the reservoir in addition to the gas. Consequently, the experimental injection of water into the reservoir was begun March 11, 1946, in Louisiana, and it was found possible to force from

6 500 to 1,000 barrels of water into the upper Pettet zone in the average intake well with surface pressures under 1,500 psi. A total of 94,942 barrels of water was put into the reservoir in 87 days, during which time the reservoir pressure in the vicinity of the input well increased somewhat. Consequently, input wells in a double row across the field (Fig. 20) at the Arkansas-Louisiana boundary line have been prepared and injection of water on an experimental basis was begun in a well in Arkansas on June 28, 1946, in accordance with plans authorized by the Arkansas Oil and Gas Commission. Injection of water into a second well was,begun July 15, Fresh water is being used (Table 19). The maximum recovery from the Arkansas extension of the Haynesville field by primary methods of production is predicated on the demonstrated relation existing between reservoir pressure and cumulative oil production, future gas-oil ratios based upon the rate of increase in gas-oil ratios experienced in the field and an abandonment pressure of 300 psi; this recovery is estimated to be 4,500,000 barrels of oil at the most. Maintenance of reservoir pressure by the return of 80 per cent of all gas produced should enable the recovery of about 6,000,000 barrels of oil at stock-tank conditions, an increase over the recovery by primary methods of 1,500,000 barrels. Maintenance of pressure by injection of gas also makes possible the recovery of 440,000 barrels of natural gasoline in addition to the oil. The injection of water, if this be done systematically throughout the reservoir, should enable the recovery of about 2,500,000 barrels of oil over and above the oil and natural gasoline recoverable by injection of gas alone.