Shut-in Well Research Articles

Lisbon Valley Anticline, Paradox Basin, Utah--Exploration and Development: ABSTRACT

In 1959, Pure Oil Company made sensational simultaneous discoveries of the first major oil and gas accumulations from the Mississippian in the Paradox fold and fault belt at Lisbon and McIntyre Canyon Units. These discoveries indicated that the tectonics of the pre-salt flowage structures in the province could and would be solved. A massive exploration program was launched, but during the intervening years, only three relatively minor discoveries have been made in pre-Pennsylvania rocks. Two of these are associated with the Lisbon structural complex. Similarities between the Persian slat anticlines and those of the Paradox basin had long been recognized and the idea of parallel, but offset, pre-salt structures was the basis on which large blocks were leased. Many operators were wary of seismic problems associated with salt flowage and(or) solution; however, Pure persevered and, in 1957, demonstrated at Big Flat field that seismic mapping was feasible and that the Mississippian could contain oil. This led the Pure's successful survey at Lisbon. Drilling has shown that the thickened salt core of the Lisbon Valley surface anticline occupies the crestal graben of an offset-toward-the-southwestern pre-salt anticline. Mississippian fault traps closed against salt have been found on the upthrown blocks on each side of the graben. Largest of these is the Lisbon Unit with 1,800 ft. of effective closure. In addition to the Mississippian, oil production has been obtained from the Devonian Ouray and McCracken but early promise of these formations as important objectives has not materialized. One well, now abandoned, has produced oil from the Paradox salt. Post-salt Pennsylvania producing potential is indicated by two shut-in wells from multiple Hermosa sandstones on the downthrown block of the surface anticline which is closed against salt. Several wells within the Lisbon Unit have also tested shows of oil on drill-stem test of the Ismay. The Lisbon Valley-Dolores trend is only one of the five major salt flowage structural trends of the Paradox basin. Traps similar those at Lisbon can be expected to be associated with other salt anticlines. A conservative estimate of the ultimate gross value of recoverable hydrocarbons from the Lisbon anticline is anticline $100,000,000. Search in similar accumulations is indeed warranted! End_of_Article - Last_Page 1571------------

A Simple Method for Correcting Spot Pressure Readings

Abstract Pressure information for use in material-balance calculations is obtained, where possible, from pressure build-up surveys in shut-in wells. Using proper extrapolation methods, static pressures are obtained which, by averaging, give the field static pressure. Often, particularly in fields with a large number of wells, only spot pressure readings are available. A graphical method is presented here which enables the determination of the corrections which must be applied to the spot readings to give an estimate of the static pressure. Although the static pressures thus obtained are not so reliable as those from build-up surveys, they are more nearly correct than the spot readings themselves for use in material-balance calculations. Introduction The average static pressure in a bounded reservoir is determined from a number of individual-well pressure measurements. Where pressure build-up curves are available, extrapolation methods such as described in Ref. 3 may be used to determine the static pressure in the drainage area of each individual well. The possibility of using pressure build-up curves presupposes that each well being surveyed is closed in during a certain period and that, during this time, a pressure recorder is left suspended in the hole. For surveys in fields with a large number of wells, this is usually not feasible for economic and other reasons. Either a large number of pressure recorders would have to be used simultaneously or, using a limited number of recorders, the time interval needed to complete a field-wide survey would be too long. The data obtained for this incomplete coverage are insufficient to permit reliable averaging of the few calculated static pressures over the entire reservoir. In many such cases another type of pressure information is available, i.e., spot pressure readings. During this type of pressure survey all wells are closed-in simultaneously and, after a reasonable shut-in time (e.g., three days), pressure readings are taken by running the recorder in and out of each successive well. These surveys, which are less expensive, are often taken at regular intervals, say once or twice a year.

A Comparison of Theoretical Pressure Build-Up Curves with Field Curves Obtained from Bottom-Hole Shut-In Tests

Abstract Interpretation of pressure build-up data obtained in the conventional manner has often been difficult because of the deviation from theoretical behavior. Major causes of this deviation have been attributed to damage and afterflow, and to fluid redistribution in the wellbore which, in extreme cases, can result in a pressure hump in the early portion of the build-up curve. Theoretical investigations show that bottomhole pressure is definitely influenced by phase redistribution in the tubing column during surface shut-in tests, and that the magnitude of the effect is sensitive to the producing gas-oil ratio and stabilized rate of flow in the well. For field experiments a wire-line tubing packer, which can be run in the tubing against a stabilized flow rate, was developed for bottom-hole shut-in tests. By use of this bottom-hole shut-in method, pressure humps previously observed in surface shut-in tests were completely eliminated and the effects of afterflow minimized. Analog and digital computer studies have been made to obtain theoretical curves for comparison with field curves, and remarkable agreement between the results of bottom-hole shut-in tests and theoretical curves has been obtained. Introduction Pressure build-up data from shut-in wells have been used by the petroleum industry to determine the permeability of the formation, to estimate wellbore damage, to evaluate the static reservoir pressure and to speculate reservoir volume. Calculation of these factors is based on methods of analysis developed for theoretical systems whose build-up curves have a characteristic shape when the wells are shut-in at the sand face. However, field curves obtained by conventional surface shut-in methods do not always exhibit this characteristic. Such factors as stratification, rock heterogeneities and irregular reservoir geometry can cause the character of a buildup curve to deviate from that predicted by theory for a simple system. In addition, all field build-up data are affected by the methods utilized in obtaining the measurements.

The Estimation of Permeability and Reservoir Pressure From Bottom Hole Pressure Build-Up Characteristics

Abstract This paper presents a simple and practical method for the estimation ofeffective permeability and reservoir pressures from the rise in bottom holepressure when a well is shut in. The equations on which the method is basedconsider a stabilized well producing from a uniform formation when flow is shutoff at the sand face followed by the unsteady state flow of a compressibleliquid from regions far from a well to points closer in during the build-upperiod. An approximation for extending the method for two-phase flow in thereservoir is also presented. In order to compare the effects of extremes in the conditions existing atthe external boundary of the reservoir, two general equations defining thebuild-up characteristics of the reservoir are shown: first, for a reservoirwith constant pressure maintained at the radius of drainage, and second, for areservoir with no influx over the radius of drainage. These equations definethe build-up characteristics for the shut-in well as functions of time, thepermeability and porosity of the drainage area, the viscosity andcompressibility of the fluid flowing, the production rate prior to shut-in, andthe radius of drainage of the well. When a well is shut in at the surface, rather than at the sand face, flowwill continue into the well bore after shut-in due to the compressibility ofthe fluids in the bore. The effect upon the build-up characteristics of thisflow into the well after shut-in has been studied by means of the electricalanalyzer. From the basic relationships and consideration of the limitations dueto continued flow after shut.in, methods have been developed for the estimationof the effective permeability of an area from the plot of the build-upcharacteristics of the well producing that area. T.P. 2849

Effect on Producing Wells of Shutting in the Offset Wells

In times of overproduction such as the operators have been strugglingagainst for the past several years it is the practice of the oil industry toshut in certain wells in order to reduce the flood of oil. The purpose of thispaper is to present certain variations in production of oil wells when theoffset wells are shut in. The scope of the study has been confined toCalifornia fields, and more especially to those of the San Joaquin Valley. The accepted definition of a shut-in well is a well where production hasbeen suspended by closing in the casinghead and tubing or by cessation of pumping. The immediate effect of such a procedure, of course, is to reduce theoil production from the lease, which is the result desired. However, it appearsthat certain types of wells vary widely in production of oil, gas and gasolineafter adjacent wells have been shut in, which variation has a very materialeffect on the ultimate recovery of oil from the property. The increase ordecrease in the oil production itself may not be of sufficient volume to occasion comment, but wide fluctuations in the gas and gasoline recovery underthe changed conditions are of the utmost importance in the future recovery of oil. The scope of this paper includes:the effect on producing oil wells ofshutting in offset wells, the wells being studied in three groups arrangedaccording to their relative stages of depletion;probable source of excessgas and the effect on the ultimate recovery of oil;suggested procedurewhen wells are shut in;methods that could be employed to prevent unduemigration of gas from the shut-in area; andthe need for future studies ofthe situation. Three Classes of Producing Oil Wells For the purposes of this paper producing wells in California have beenarranged in three groups according to the age of the well, or to the relativestage of depletion of the producing zones. The first group consists of thosewells with a high fluid level, or in other words those wells whose fluid levelsare a considerable distance above the top of the perforations.