Showing papers presented at "Formal Methods in 1974"

Oil Production from Fractured Reservoirs by Water Displacement

Abstract: A study has been made of the flow behavior of fractured oil reservoirs produced by water displacement. A 2-dimensional numerical model capable of simulating flow of water and oil in the matrix blocks as well as in the fractures has been developed. The validity of the model has been checked against data from a laboratory experiment involving a matrix-fracture system. Good agreement was observed between the laboratory and simulation results. By means of numerical simulation, the effects of production rate and fracture flow capacity on the production history and ultimate oil recovery of a fractured system have been evaluated. Results are presented for a single matrix-block system where the block is surrounded by horizontal and vertical fractures. Production rates ranging from 0.05 to 5 times the gravity reference rate of the matrix, and fracture flow capacities ranging from 0.1 to 10 times the flow capacity of the matrix are included in the investigation. (32 refs.)

Formation fracturing with foam

Abstract: Over 60 wells have been treated with hydraulic fracturing techniques, with foam as the fracturing fluid. These foams contained as much as 95% gaseous phase; most treatments used foams with gas contents in the 65% to 85% range. Foam has several desirable properties for use as a fracturing fluid: high sand-carrying and sand-suspending capability, low fluid loss, low hydrostatic head, low pressure drops due to friction, quick fluid recovery, low formation damage, and no reduction of fracture conductivity due to fluid ingredients. Most applications of foam as a fracturing fluid have been in low permeability gas reservoirs. However, several oil reservoirs also have been successfully treated. Cost of the treatment is approx. the same or slightly less than a treatment with conventional fluids of comparable volume and rate. (25 refs.)

Optimizing Gas-Lift Systems

Abstract: The most profitable distribution of gas to wells in a continuous flow gas-lift system can be determined by an analytical procedure. The procedure utilizes well test information and calculations of vertical 2-phase flow behavior to predict individual well producing rate responses to changes in gas input rate. The optimum distribution of the available gas can be calculated based on each well's contribution to the profit for the system. A computer program was developed to perform the calculations for the procedure. This program has been used in a Venezuela field with 1,500 gas-lift wells. A modified version of the program has been used in a Texas field containing 150 gas-lift wells.

Simplified Method for Gas-Lift Well Problem identification and Diagnosis

Abstract: A system is described for detecting and diagnosing problem gas-lift wells based on well test data. Wells are screened so that only those with abnormal producing conditions are identified for further analysis. The analysis utilizes well tests and installation specifications to define troubles and predict efficient gas injection rates. This method circumvents the need for numerous flowing pressure and temperature traverses in continuous flow gas-lift facilities.

Laboratory investigations in the Use of Polymers in Low Permeability Reservoirs

Abstract: Many of the reservoirs under consideration for polymer injection contain very low permeability sandstones and limestones. Because of the large size of the polymer molecules considered, the use of polymers in tight formations must be closely scrutinized. Laboratory results investigating the viability of polymer treatment in low permeability sandstone and carbonate field cores are presented. Polymer resistance factor, residual resistance factor, and retention data are reported for a partially hydrolyzed polyacrylamide and for a new copolymer of acrylamide. In comparing the field reservoir cores evaluated, a considerable difference was seen in the behavior of polymers in sandstone vs. limestone. The hydrolyzed polyacrylamide evaluated was able to penetrate low permeability limestone cores but caused severe plugging in sandstone cores of similarly low permeability (K/sub air/ = 7 md - 59 md). In the case of sandstone, the copolymer of acrylamide was able to penetrate low permeability cores while hydrolyzed polyacrylamide of the same viscosity could not. (27 refs.)

Recovery Optimization Through Infill Drilling Concepts, Analysis, and Field Results

Abstract: Theoretical concepts and some supporting mathematical model and field performance data are given which demonstrate factors that can be involved in recovery increases by infill drilling. Many of these factors relate to various reservoir heterogeneities and are quantitatively more important in fluid injection projects. Recovery increase by infill drilling of low-permeability waterflood projects can be due to as many as 9 different factors with varying degrees of technical difficulty to specifically quantitize. However, based on performance and certain theoretical knowledge and concepts, reasonable factors involving judgment can be developed as to percent of original oil-in-place recovery increase. (15 refs.)

Use of Guar Gum and Synthetic Cellulose in Oilfield Stimulation Fluids

Abstract: The use of polysaccharides to alter the rheological properties of aqueous fracturing fluids has been a common practice for many years. In certain cases, the inherent properties of these natural and synthetic polymers have been negated by their sensitivity to adverse parameters present in both the base fluid and the formation. Some of these parameters have been identified as ionic strengths, transition metal concentrations, high bottom-hole temperatures, and chemical redox systems. Chemical solutions to these problems, which eliminate or minimize the detrimental effects, have been developed for field operations. Once the problem has been recognized and defined, an appropriate chemical treatment will usually make the field water usable, bypassing the necessity of finding an alternate supply. Higher base viscosities of the polymer sol and less polymer sensitivity to the ionic strength of the field waters have been noted in several instances. Exceptional polymer stability at higher temperatures has been obtained with one procedure.A description is presented of the various polysaccharide systems, their sensitivities, and the methods employed in countering these sensitivities. (35 refs.)

Heavy Oil Recovery by Steam-Driven Hydrocarbon Slugs from Linear Porous Media

Abstract: This work was principally concerned with an experimental study of oil recovery from a porous medium by the injection of a light hydrocarbon slug, followed by a steam slug, which is in turn driven by a conventional waterflood. An attempt was made to simulate the experiments by use of a cell model. The experiments involved fluid displacements in 2 glass bead packs having a rectangular internal cross-section of 1.75 x 3.75-in. and 48-in. length, overlain and underlain by 1.5 ft thick sand packs to simulate the adjacent formations. It was found that the light hydrocarbon slug injected prior to the steam slug in a core initially containing a residual oil saturation improved the oil recovery as compared to a straight steam slug run. It is concluded that from the recovery ratio (volume of oil recovered divided by hydrocarbon slug volume) point of view, it is advantageous to use a low viscosity light hydrocarbon slug, and a small slug size.

Improved Injectability of Biopolymer Solutions

Abstract: Injectability of biopolymer produced by the organism Xanthomonas campestris can be significantly enhanced by the use of proper mixing techniques, adequate surface preservation from microbial attack, and the use of clean bacteria-free injection systems and source waters. An evaluation of filtration and clarification methods and costs has shown that large reduction in the number or size of cellular material can be obtained at minimal costs.

An underground coal gasification experiment, Hanna, Wyoming

Abstract: In the fall of 1972, the U.S. Bureau of Mines began an experiment to investigate the technologic, economic, and environmental considerations of underground gasification of a W. subbituminous coal. The gasification site is near the town of Hanna, Wyo., approx. 70 miles northwest of Laramie. The test results indicate that gas volumes and gas heating values have fluctuated over a wide range depending on operating conditions. The ranges have been from 50,000 to over 3 MMscfd of produced gas with a composite heating value from 30 to 465 btu per scf. Even though these fluctuations have occurred, a semisteady state condition existed for a 6-mo. period. From Sept. 1973 through Feb. 1974, a low btu gas averaging about 130 btu per scf was produced at an average rate of 1.6 MMscfd. A material balance made during this period indicated: (1) there was little or no underground gas leakage from the site; (2) about 80 bbl of formation water were consumed each day; (3) between 13 and 46 tons of dry coal were affected each day depending on the assumptions made; and (4) from 23 to 65% of the energy of the coal being subjected to carbonization and/or gasification is beingmore » recovered.« less

Cold Waterflooding a Warm Reservoir

Abstract: A thermal simulation program and a theoretical analysis consider the effects of cold waterflooding a warm reservoir. For the conditions investigated, the injected water quickly cools the region surrounding the wellbore and accounts for the major part of the pressure drop across the system. Heating the injected water or fracturing the formation each decrease the pressure drop and can be used to avoid an uncontrolled fracture or the need for costly, high-pressure surface injection equipment. The study showed that thermal effects can play a major role in the economics of waterflooding projects.

Sand Consolidation Systems Placed with Water

Abstract: Sand consolidation systems using resinous materials have been developed which require only water (brines) in the placement procedures. The use of water-treating fluids is solving several important problems in the field associated with current consolidation methods which use oil placement fluids. The brine-treating fluids are easily handled and have presented no disposal problems, particularly on offshore locations. The desirable weighting and no fire hazard characteristics of brines have improved safety. These aqueous fluids can be used in gas and nonpotable water (source or injection) wells where it is undesirable to use oils. Waters to prepare the brine-treating solutions are readily available. Formation brine, fresh water, bay and sea waters have all been used. Laboratory results and field development data on 14 initial applications are presented.