Showing papers in "Journal of Petroleum Technology in 1988"

PVT Correlations for Middle East Crude Oils

Abstract: Les donnees Pression-Volume-Temperature (PVT) sont analysees a partir de 69 echantillons de fluide de fond de puits provenant de 69 reservoirs du Moyen Orient. 160 donnees numeriques sont utilisees pour developper la correlation de la pression du point de bulle avec la proportion gaz/huile, la densite relative du gaz dissout et la densite relative de l'huile dans le reservoir. Deux autres correlations sont developpees: celle du facteur volumetrique de fonds a la pression du point de bulle et celle du facteur volumetrique total de fond a des pressions inferieures a celle du point de bulle en fonction de la proportion gaz/huile, de la densite relative du gaz dissout, de la densite relative de l'huile dans le reservoir, de la temperature et de la pression uniquement pour la derniere correlation

Augmentation of well productivity with slant and horizontal wells

Abstract: This paper presents an equation to calculate the productivity of horizontal wells and a derivation of that equation using potential-fluid theory. This equation may also be used to account for reservoir anisotropy and well eccentricity (i.e., horizontal well location other than midheight of a reservoir). The theoretical predictions were used to calculate the effective wellbore radius and the effective skin factors of horizontal wells. Laboratory experiments with an electrical analog were also conducted. These laboratory experimental data and also the laboratory data available in the literature show good agreement with the theoretical equation, indicating its accuracy. The paper also compares vertical-, slant-, and horizontal-well productivity indices, assuming an equal drainage area. In addition, the comparison also assumes an equal reservoir contact area for slant and horizontal wells. The results show that in a 100-ft (30.48-m) -thick reservoir, horizontal-well productivities are two to five times greater than unstimulated vertical- or slant-well productivities, depending on reservoir anisotropy. Conversely, in a 400-ft (122-m) -thick reservoir, slant wells perform better than horizontal wells if vertical permeability is less than horizontal permeability. Horizontal wells perform significantly better than vertical wells in reservoirs with gas cap and/or bottomwater. This study reports an equation to compare horizontal-more » and vertical-well gas-coning tendencies. The results indicate that horizontal wells are suitable for reservoirs that are thin, show high vertical permeability, or exhibit gas- and water-coning problems. The equations reported should be useful in initial evaluation of a horizontal-well drilling proposal.« less

Relative-Permeability Measurements: An Overview

Abstract: Significant advances have been made in methods for accurate measurements of saturations and fluid distributions. Further research is needed to reduce (or properly account for) capillary end effects, to control hysteresis, and to minimize wettability changes involved in flow experiments. Studies are needed on modeling complex displacements in reservoirs with flow tests performed at idealized laboratory conditions. Similarly, improvements in interpretation of laboratory data and in scaling up for field use are still required. Until additional advances in technology are made, the best course of action is to generate both steady- and unsteady-state laboratory data, under simulated reservoir conditions, on carefully selected and preserved cores.

Effects of Perforation-Entry Friction on Bottomhole Treating Analysis

Abstract: Analysis of field and laboratory data shows that variations in pressure drop due to changing perforation entry friction tends to strongly influence the prediction of fracturing treatment performance. This paper presents experimental data on perforation entry friction as it affects fracturing treatment design. Pre- fracturing treatment planning practices include examination of numerous treating pressure charts in an effort to determine formation type curves, which are used to anticipate fracturing treatment performance and screenout modes. Perforation entry friction may vary greatly because of erosion of the perforation and near wellbore fracture, and this changing friction pressure is often not properly accounted for in planning. This paper presents the following: 1.Discussion and data (laboratory and field showing the degree of perforation erosion encountered in fracturing operations. 2. Proposed guidelines to determine when to alter proppant schedule to account for proppant erosion to perforations, cement sheath, and formation.

Improved calculations for viscous and gravity displacement in matrix blocks in dual-porosity simulators

Abstract: This paper presents two innovations to improve the mathematical representation of viscous and gravity displacement from matrix blocks in dual-porosity simulators. The first improvement accounts for viscous displacement and convective mass transport in matrix blocks caused by potential gradients in the fracture network. Computation time is not significantly increased compared with current dual-porosity simulators. The second improvement provides two computationally efficient methods to refine simulation of gravity displacement in the matrix. Examples show that the improvements are highly desirable in many situations.

Wettability and Adsorption Characteristics of Crude-Oil Asphaltene and Polar Fractions

Abstract: This study relates the chemical composition of the polar compounds of crude oil to the wettability of rock/oil/brine systems. Adsorption properties of polar and asphaltene fractions were evaluated to determine their effects on wettability. Polar compound fractions were found to cause an oil-wet state on Berea sandstone, but the effects were not a function of the polar-fraction concentration. The concentration of nitrogen/sulfur compounds in six crude-oil polar fractions correlated with the wettability of the polar fractions on Berea sandstone. Langmuir-type adsorption on Berea sandstone was observed in adsorption studies of the asphaltene and polar fractions. Additional analysis with brien-saturated Berea sandstone resulted in adsorption values up to three times less than that for dry Berea. The amount of polar fraction adsorbed on brine-saturated berea sandstone correlated with crude-oil wettability.

Development of Heavy-Oil Reservoirs

Abstract: Although complex categorizations are in vogue, ''heavy oils'' can be defined simply in terms of their flow properties in the reservoir-e.g., a 100-cp (100-mPa.s) or greater viscosity. Such heavy oils are major world hydrocarbon resource that is exploited where indigenous demand exists. Efficient methods of production require enthalpy input to the reservoir by hot-fluid injection or by creation of heat in the reservoir. Heat losses must be minimized to achieve maximum production efficiency. The widely used cyclic-steam-injection process is examined analytically to indicate which parameters govern successful exploitation. Steamflood and in-situ combustion techniques are discussed with reference to recent developments. Heavy-oil recovery from the more difficult carbonate reservoirs, such as those of the Middle East, is reviewed and potential production mechanism are examined. Production techniques are described together with export handling schemes.

Role of asphaltenes in compositional grading of a reservoir's fluid column

Abstract: The relationship between compositional variations induced by gravity and reservoir-fluid phase behavior has been investigated. In light oils (stock-tank oil gravity less than or equal to0.85 g/cm/sup 3/ (greater than or equal to35/sup 0/ API)), strong compositional grading will occur if the reservoir fluid is near critical. In heavier oils, compositional grading is caused by the segregation of asphaltenes, resulting in variation in oil viscosity and the possibility of tar-mat formation.

Sulfur Solubility in Sour Gas

Abstract: It is well known that sulfur is soluble in sour gas and often precipitates during production if the temperature and pressure decrease. Of more significance is the possibility of sulfur precipitation in the reservoir as the pressure is reduced. This applies particularly to high-temperature reservoirs, where sulfur is believed to be more viscous, or to moderate-temperature, low-permeability reservoirs. In either case, sulfur precipitation can impair well productivity and thus the economics of reserve depletion. In the U.S., large sour-gas reserves with reservoir temperatures between 390 and 500 K (242 and 440/sup 0/F) are being exploited. The purpose of the work was to obtain sufficient sulfur-solubility data in sour gas to develop a widely applicable predictive model of sulfur solubility vs. sour-gas conditions. The data include the effects of temperature, pressure, and gas composition, including variations in the amount and composition of gas-condensate components. Pressures and temperatures ranged from 6.7 to 155 MPa (970 to 22,500 psi) and 394 to 486 K (250 to 415/sup 0/F), respectively. The influence of H/sub 2/S on the melting curve was also reported. The value of the experiments was two-fold: to provide information that would allow production and reservoir engineers to predict more reliably themore » reservoir pressure at which sulfur will precipitate and to yield design data for production systems in which sulfur plugging problems in tubing, flowlines, and production facilities could be avoided.« less

PDC Drill Bit Design and Field Application Evolution

Abstract: This paper traces the development of polycrystalline diamond compact (PDC) bits from their introduction in 1973. Such design features as body materials, crown profiles, cutter density, and cutter exposure and their effect on bit performance are discussed. In addition, the paper reviews various aspects of bit applications engineering, including bit hydraulics, drilling fluids, directional behavior, and formation types.

Polycrystalline Diamond: Manufacture, Wear Mechanisms, and Implications for Bit Design

Abstract: This paper focuses on the failure modes of polycrystalline-diamond-compact (PDC) cutters and discusses efforts to improve impact resistance, thermal stability, and hydraulic cooling. Composite-transition-layer technology has made possible a new generation of polycrystalline-diamond (PCD) -enhanced inserts that can be used in percussion and roller-cone applications.

Fracturing-fluid additives

Abstract: Fracturing-fluid additives serve two purposes: to enhance fracture creation and proppant-carrying capacity and to minimize formation damage. Additives that assist fracture creation include viscosifiers, temperature stabilizers, pH-control agents, and fluid-loss-control materials. Those used to minimize formation damage are gel breakers, biocides, surfactants, clay stabilizers, and gases. This paper discusses the qualities and applications of each of these additives.

Use of the Pressure Derivative for Diagnosing Pressure-Transient Behavior

Abstract: The combined plot of log pressure change and log derivative of pressure with respect to superposition time as a function of log elapsed time was first introduced by Bourdet et al. as an aid to type-curving matching. Features that are hardly visible on the Horner plot or are hard to distinguish because of similarities between one reservoir system and another was easier to recognize on the pressure-derivative plot. Once the patterns have been diagnosed on the log-log plot, specialized plots can be used to compute reservoir parameters or the data can be matched to a type curve.

Minimizing Damage to a Propped Fracture by Controlled Flowback Procedures

Abstract: Severe fracture-conductivity damage can result from proppant crushing and/or proppant flowback into the wellbore. Such damage is often concentrated near the wellbore and can directly affect postfracture performance. Most of the time severe fracture-conductivity damage can be minimized by choosing the correct type of proppant for a particular well. In many cases, however, this is not enough. To minimize excessive crushing or to prevent proppant flowback, it is also necessary to control carefully the flowback of the well after the treatment. Specific procedures can be followed to minimize severe fracture-conductivity damage. These procedures involve controlling the rates at which load fluids are recovered and maximizing backpressure against the formation. These procedures require much more time and effort than is normally spent on postfracture cleanup; however, the efforts could result in better performance.

Computed Tomography as a Core Analysis Tool: Applications, Instrument Evaluation, and Image Improvement Techniques

Abstract: In recent years, the use of computerized tomography (CT) to characterize two-phase fluid flow through porous media has become increasingly popular. This paper describes a different application of CT: it use as a core analysis tool. The advantages and disadvantages of the different technological generations of commercial medical CT scanners available as core analysis instruments are also discussed. Additionally, methods are presented for improving images and reducing CT-number errors inherent in the scanning of high-density rock samples on instruments whose software was designed for the scanning of the low-density human patients.

The Role of Noncondensable Gas in Steam Foams

Abstract: Field tests suggested that a steam-foam drive is more effective when nitrogen, methane, or the like is added to the formulation. A plausible explanation is that foam lifetime is longest when transport of noncondensable gas limits mass transfer between steam bubbles. On the basis of this hypothesis, a method to estimate the amount of noncondensable gas to be included is presented.

The CO2 Huff 'n' Puff Process in a Bottomwater-Drive Reservoir

Abstract: Two CO/sub 2/ huff 'n' puff projects were conducted in the 4,900-ft (1495-m) Reservoir (BA) Sand Unit (4900' R(BA)SU), Timbalier Bay field, Louisiana. This reservoir is a bottomwater-drive reservoir unit a 26/sup 0/ API (0.9-g/cm/sup 3/) oil gravity and 18% primary oil recovery. Before CO/sub 2/ injection, both project wells were gas lifting more than 1,000 BFPD (160 m/sup 3//d fluid) with 99% water cuts. After CO/sub 2/ injection, the production from each well increased to 200 BOPD (32 m/sup 3//d oil). This paper discusses the CO/sub 2/ huff 'n' puff process, specific reservoir characteristics, and project evaluation.

Criteria for gas-lift stability

Abstract: Severe flow instability (heading or annulus heading) is known from operations of gas-lift systems. Here, two simple stability criteria are developed and compared with reported field data. The stability problems experienced for the cases examined would have been identified with these criteria and corrected at the design stage.

Influence of an immobile or mobile saturation on non-Darcy compressible flow of real gases in propped fractures

Abstract: The effects of immobile and mobile liquid saturations on the non-Darcy flow coefficient in propped fractures have been investigated. It was observed that an immobile liquid saturation of up to 20% PV can triple the non-Darcy flow coefficient and a small mobile liquid saturation will increase the non-Darcy flow coefficient by nearly an order of magnitude (over that of the dry case). The linear relationship between the logarithm of the non-Darcy flow coefficient and the logarithm of the proppant permeability for propped fractures, as proposed by Cooke, is shown to be invalid in the presence of an immobile or mobile liquid saturation. Constants are presented that can be used to obtain a more accurate approximation than has previously been available on the non-Darcy flow coefficient for single-phase flow in fractures propped with 10/20- and 20/40-mesh Ottawa sand. The experimental data obtained from this research was compared with those of others reported in the literature.

Birba Field PVT Variations Along the Hydrocarbon Column and Confirmatory Field Tests

Abstract: This paper describes a practical application of thermodynamic modeling that indicated that the PVT properties of the reservoir fluid in the Birba field were strongly depth-dependent, explaining the presence of significantly undersaturated oil only 200 m (655 ft) below a gas cap. Field tests confirmed the thermodynamic model to be correct. Furthermore, this paper discusses the options for field development, including the consideration of possible benefits of (developed) miscibility when gas is injected.

Production performance analysis of horizontal drainage wells for the degasification of coal seams

Abstract: The production performances of horizontal drainage wells for the degasification of coal seams have been investigated with a multidimensional, two-phase coal-seam degasification model. The model is written in rectangular coordinates, can handle a number of horizontal wells, and operates in a one-, two-, or three-dimensional (1D, 2D, or 3D) mode. The model accommodates multiple horizontal boreholes originating from a common vertical shaft or horizontal boreholes being drilled from the peripheries of the reservoir. In consideration of the relatively thin but large lateral extent of coal seams, flow dynamics around a horizontal borehole is described in elliptic flow geometry. The nonlinear system of equations generated by the finite-difference approximation is solved fully implicitly with Newton's iteration. A series of computer runs was conducted systematically to demonstrate the relative significance of different reservoir and fluid characteristics on the negative and positive decline features of horizontal drainage wells. Along these lines, the effects of coal-seam properties - such as thickness, porosity, permeability, and sorption characteristics - and horizontal borehole parameters - such as hole diameter, penetration length, and positioning of the borehole - have been isolated to understand the role of each individual parameter on the production performance of horizontal drainage wells. Contrarymore » to the design of a vertical fracture, the orientation of the horizontal borehole with respect to face and butt cleats is controllable. Results of another series of runs are presented for different orientations of horizontal boreholes with respect to the principal directions of the natural fracture network to maximize the recovery of methane from coal seams through horizontal boreholes.« less

The Origins of Anisotropy (includes associated papers 18394 and 18458 )

Abstract: Apres avoir defini l'anisotropie, l'auteur etudie les consequences de l'anisotropie de la permeabilite, son importance au cours d'un ecoulement monophasique a travers un milieu diphasique, ses representations par des tenseurs et ses causes geologiques

Reservoir-fluid phase behavior and volumetric prediction with equations of state

Abstract: The use of several cubic equations of state (EOS) in predicting vapor/liquid equilibria (VLE) and volumetric behavior of reservoir-like and real reservoir fluids is discussed, and the difference between these equations is examined. It is shown that these equations can reliably predict phase behavior of complex reservoir crude and gas-condensate systems away from the critical and retrograde regions. The cubic equations that the authors examined predict nearly the same KAPPA values. The volumetric prediction, however, is different from one equation to another.

Stress-Intensity Factor and Fracture Cross-Sectional Shape Predictions From a Three-Dimensional Model for Hydraulically Induced Fractures

Abstract: An efficient three-dimensional (3D) fracture model was developed that can be applied to arbitrary planar cracks with Mode 1 stress singularity at the fracture tip. Surface stress, thermally induced stress, and poroelasticity were included. In addition, the elasticity constants can be varied between elements. A parameter study was conducted with the model to evaluate the stress-intensity factor, the evolving shape of the fracture, and fracture width. The study includes the borehole effect, fracture migration, fracture barriers, fracture cross-sectional shape, fracture front shape and its stress-intensity factor, and evaluation of the validity of some simplified models. Further work on the details of the theory, algorithm, accuracy, and efficiency of the 3D fracture model is in progress.

Fracture Conductivity in Hydraulic Fracture Stimulation

Abstract: Etude de l'influence de la permeabilite des materiaux d'etaiement de la fracture de la contrainte de fermeture de la fracture, de l'ecoulement multiphasique, de l'endommagement du aux fluides de fracturation, de l'accumulation des residus et du gâteau de filtration sur l'amelioration de la productivite au cours des traitements de stimulation de la fracture

Status of Polycrystalline-Diamond-Compact Bits: Part I Development(includes associated papers 19032 and 19900 )

Abstract: Polycrystalline-diamond-compact (PDC) bits have become an established new generation of oilfield bits, particularly for drilling soft-to-medium-hard, nonabrasive formations. The development of these bits is still at an exciting stage. The state of the art in PDC cutters and bits is discussed and illustrated by a rich source of fairly recent literature. A look into the future is attempted in light of the bits' potential.

Fahud field review: a switch from water to gas injection

Abstract: The water injection schemes implemented in the Fahud field during the early 1970's led to poor recoveries because the reservoirs were both fractured and oil-wet. On the basis of the results of a thorough performance review, it was decided in 1983 to promote gas/oil gravity drainage fully by drilling rows of downdip producers and switching completely from water to gas injection. This paper investigates the reasons behind each stage of development and reviews recent efforts to evaluate the future production potential through the use of dual-porosity simulators.

A new approach to the hyperbolic curve

Abstract: An efficient and timesaving approach to hyperbolic-decline-curve analysis has been developed that has made it possible to determine the hyperbolic b exponents characterized by thousands of wells. After extensive use of the technique, the authors concluded that the range of the b exponent previously prescribed by Arps is too narrow.

High-Rate Artificial Lift

Abstract: This paper summarizes the major considerations in the selection, design, installation, operation, or repair of high-rate artificial-lift systems. The major types of artificial lift - sucker-rod pumps, gas-lift systems, electrical submersible pumps, hydraulic pumps and jets, and hydraulic turbine-driven pumps - will be discussed. An extensive bibliography of artificial-lift papers is included.

Reservoir description from seismic lithologic parameter estimation

Abstract: Modern three-dimensional (3D) seismic data assist not only in delineating reservoir geometry, but also in predicting porosity and lithology variations away from well control. This case study of an oil-producing channel sand in the Taber/Turin area, Alta., Canada illustrates the improvement in reservoir characterization achieved with an integrated approach incorporating both well and seismic information.