Showing papers in "Spe Production Engineering in 1992"

A Unified Model for Predicting Flowing Temperature Distribution in Wellbores and Pipelines

Abstract: This paper presents a general and unified equation for flowing temperature prediction that is applicable for the entire range of inclination angles. The equation degenerates into Ramey's equations for ideal gas or incompressible liquid and into the Coulter and Bardon equation, with the appropriate assumptions. This work also proposes an approximate method for calculating the Joule- Thomson coefficient for black-oil models

Fines migration and formation damage; Influence of pH and ion exchange

Abstract: This paper elucidates the influence of pH and ion exchange on formation damage caused by fines migration. The experimental results affect waterflooding, design of drilling muds, and alkaline flooding. In-situ release of naturally existing fines (generally clays) results form change sin colloidal conditions of the permeating fluid. Such processes can cause extensive formation damage in sandstones, thereby reducing oil production. The authors' recent studies clearly indicate that the release process is started by a combination of high pH, leading to drastic permeability reductions. These results therefore provide new insight into the phenomenon of formation damage caused by water sensitivity or injection of incompatible brines. The authors also describe a unified approach to understanding these results and the findings of previous investigators.

An improved finite-difference calculation of downhole dynamometer cards for sucker-rod pumps

Abstract: This paper presents a finite-difference representation of the wave equation developed for diagnostic analyses of sucker rod pumping systems A consistent method of computing the viscous damping term associated with the damped-wave equation is also presented

Barium and Strontium Sulfate Solid-Solution Scale Formation at Elevated Temperatures

Abstract: Barium sulfate scale occurrence is a severe production problem in North Sea oil operations. Barium sulfate is often accompanied by strontium sulfate to form a completely mixed scale called (Ba,Sr)SO{sub 4} solid solution. This paper describes a laboratory study carried out at 70{degrees} C to examine (Ba,Sr)SO{sub 4} solid-solution scale formation in porous media and the formation damage resulting from the mixing of two incompatible waters. The paper is a continuation of the previously reported room-temperature work. Results of experiments carried out at the elevated temperatures again demonstrate that substantial scale deposition can occur in a rock core and can cause considerable decline of rock permeability as a result of concurrent flowing of two incompatible waters.

Effect of Foams Used During Carbonate Acidizing

Abstract: Although acidization has been used successfully for many years to increase the productivity of petroleum wells in carbonate formations, demands on the performance and application of the acidizing process are increasing. This paper investigates a method of in-situ foam generation that allows deeper wormhole penetration yet uses less acid than conventional methods. The dissolution patterns were imaged with neutron radiography, which provided an in-depth understanding of the effects of foam and other critical parameters. Results show that foam is effective in promoting efficient stimulation, even at low acid injection rates.

Scale Formation in Reservoir and Production Equipment During Oil Recovery: An Equilibrium Model

Abstract: This paper presents a reliable model for the solubility products of scale-forming minerals. Our model solubilities are in relatively good agreement ({plus minus}5% to 10%) with the most reliable solubilities in aqueous solutions of up to twice the seawater concentration at temperatures of 20 to 150{degrees} C and pressures up to 40 MPa. An equilibrium mode for the reactions responsible for scale formation is developed. The CO{sub 2} equilibria between the gas, oil, and water phases and in the water phase itself are considered. By combining a hydrodynamic model for the transport of water through an oil reservoir during waterflooding with the proposed equilibrium model, we can estimate the amount of precipitate formed in the reservoir.

Evaluation of Fracture Asymmetry of Finite-Conductivity Fractured Wells

Abstract: This paper presents a graphical technique to evaluate asymmetry of hydraulically fractured wells. This technique is based on a new analytical solution for the pressure behavior of a finite-conductivity, asymmetrically fractured well during the pseudolinear flow period and the known bilinear flow solution. A semianalytical solution for transient flow toward finite-conductivity, asymmetrically fractured wells producing at constant rate is also presented. This solution was used with the analytical solution to analyze the pseudolinear flow pressure behavior. An expression relating dimensionless fracture conductivity, C{sub fD}, and asymmetry factor, a, with a parameter calculated from analysis of well-test data, {beta}{sub a}, was developed by combining the pseudolinear and bilinear flow solutions; a graph of a vs. {beta}{sub a} with C{sub fD} as a parameter is then constructed. The parameters {beta}{sub a} and C{sub fD} are calculated as follows: {beta}{sub a} = 0.309 m{sup 2}{sub bf}/(b{sub Lf}m{sub Lf}) and C{sub fD} = 2.944 m{sub Lf}m/m{sup 2}{sub bf}, with m{sub bf} as the slope of the bilinear {Delta}p-vs-t{sup 1/4} straight line, m{sub Lf} and b{sub Lf} as the slope and intercept of the pseudolinear {Delta}p-vs-t{sup 1/2} straight line, respectively, and m as the slope of the semilog {Delta}p-vs.-log t straight line obtained during themore » pseudoradial flow period. Correlations developed apply indistinctly to oil and gas wells. Published field data were reanalyzed with the technique presented here and asymmetry was detected.« less

A new method for predicting friction pressures and rheology of proppant-laden fracturing fluids

Abstract: The prediction of friction pressures for proppant-laden fracturing fluids requires estimatons of both the base-gel friction factor and the effect of proppant on fluid rheology. This paper introduces two new expressions, each theoretically based with constants determined from data, that address these two issues for hydroxypropyl guar (HPG)-based fracturing fluids in laminar and turbulent flow. The paper first introduces a new expression for the turbulent friction factor of HPG base gels. This implicit expression for the friction factor is more theoretically correct and requires one less empirical constant than explicit forms currently used

Interpretation and Theoretical Modeling of Scale-Inhibitor/Tracer Corefloods

Abstract: This paper describes a theoretical approach to determine the inhibitor dynamic adsorption isotherm from coreflood experiments. The main feature of the isotherm that contributes principally to the long squeeze life is highlighted. The problems of modeling near-well squeeze treatments and an improved simulator are discussed.

Effect of Bacterial Polysaccharide Production on Formation Damage

Abstract: This paper reports that in-situ growth of cellular material is known to cause formation damage. Bacterial reproduction and polysaccharide production are the key factors that segregate bacterial formation damage from fines and particulate damage. Carefully controlled experiments conducted on both high- and low-permeability ceramic cores showed that bacteria can plug the pore space and damage the cores. However, further experimentation demonstrated that polysaccharide production is largely responsible for this damage. This conclusion is based on a comparison of two experimental systems: core plugging from bacterial replication and polymeric production and plugging of the porous medium caused solely by cell division with no polysaccharide production. In light of these results, the interpretation of reservoir plugging resulting from the presence of bacteria requires further scrutiny.

A Unique Method for Perforating, Fracturing, and Completing Horizontal Wells

Abstract: This paper describes the evolution, laboratory testing, and field installation of a completion system developed to perforate, fracture stimulate, and isolate multiple zones in North Sea horizontal wells. This system is designed to reduce overall completion time and well control problems significantly and to allow selective zone control in production and restimulation phases. The field performance of this system is compared with that of previously used methods

Encapsulated Breaker for Aqueous Polymeric Fluids

Abstract: Persulfates are commonly used as breakers for aqueous fluids viscosified with guar or cellulose derivatives. These breakers are necessary to minimize permeability damage to proppant packs at temperatures where there is little thermal degradation of the polymers. Unfortunately, dissolved persulfates are much too reactive, even at moderate temperatures (140 to 200{degrees} F), to be used at concentrations sufficient to degrade concentrated, high-molecular-weight polymers thoroughly. Technology described in this paper was used to produce a delayed breaker. The breaker is prepared by encapsulating ammonium persulfate (APS) with a water-resistant coating. The coating shields the fluid from the breaker so that high breaker concentrations can be added to the fluid without causing the premature loss of fluid properties, such as viscosity or fluid-loss control. Critical factors in the design of encapsulated breakers (such as coating barrier properties, release mechanisms, and reactive chemical properties) are discussed. The effects of encapsulated breaker on fluid rheology were compared for several encapsulated persulfates.

Tip screenout fracturing applied to the Ravenspurn South gas field development

Abstract: Tip screenout (TS) fracturing is a means of creating greater propped fracture widths and hence fracture conductivities than can be achieved by conventional fracture treatments. This allows more cost-effective stimulations of higher-permeability reservoirs, especially where non-Darcy pressure losses are significant. This paper presents a procedure to design TSO schedules and reviews field results from the Ravenspurn South gas field, which was developed between 1988 and 1989. Evidence is provided to support the view that TSO pressure responses are indeed the result of processes occurring close to the fracture tip, rather than slurry-enhanced viscosity effects along the fracture length.

Case study of the effectiveness of nitrogen foam and water-zone diverting agents in multistage matrix acid treatments

Abstract: Several oil wells producing water have been stimulated successfully with multistages of mud acid, nitrogen foam, and water-zone diverting agents. This procedure has improved well performance significantly while having little or no effect on post-treatment water production. The diverters' effectiveness was analyzed with radioactive tracers, gamma spectroscopy logs, and surface pressure equipment. Results indicate that water-zone diverters and nitrogen foam are effective diverters when used in matrix acid stimulations. Case histories and associated data are included in this paper

Phase splitting of wet steam in annular flow through a horizontal impacting tee

Abstract: Phase splitting occurs during gas/liquid two-phase flow through pipe junctions and causes a gas/liquid mass ratio in the outlet legs of the junction that is different from that at the inlet. In steamflood distribution networks, this results in different steam qualities at the outlets of a junction than at the inlet. This, in turn, results in a heat distribution not in accordance with the mass distribution in the outlets of the tee. Because heat management of a steamflood project is important for both economic incentives and ultimate recovery, phase splitting must be understood and controlled. This paper presents the results of an experimental investigation conducted on phase splitting of wet steam during annular flow through a horizontal 2-in

Application of curable resin-coated proppants

Abstract: Laboratory investigation of the interactions between fracturing fluids and resin-coated proppants (RCP's) revealed (among other conclusions) that RCP's are incompatible with oxidizing breakers. Areas covered included RCP effect on fluid rheology, fluid relationship to RCP strength, theoretical study of required RCP strengths to prevent flowback, and experimental measurement to establish minimum strength

Incorporation of 2D fluid flow into a pseudo-3D hydraulic fracturing simulator

Abstract: Pseudo 3D (P3D) hydraulic fracturing models often overpredict fracture height for a poorly contained fracture. This is caused partly by either the neglect of the fluid flow component in the vertical direction or a crude treatment of the 2D fluid flow in the fracture as 1D flow in the vertical direction in the fracture-height calculation. This paper presents a height-growth model that adopts a flow field more representative of the actual 2D flow in a fracture. In this model, the fracture is divided into two regions: an inner region where the flow direction is nearly horizontal, and an outer region where the flow field is approximated by a radial flow from an imaginary source. The governing equations for determining height growth rate and the numerical method for solving these equations are described.

Breaker concentrations required to improve the permeability of proppant packs damaged by concentrated linear and borate-crosslinked fracturing fluids

Abstract: This paper reports on the concentrations of an oxidative breaker required to reduce significantly the proppant-pack permeability damage caused by aqueous hydraulic fracturing fluids. Long-term, proppant-pack permeability testing was used to evaluate linear and borate-crosslinked gels. Results indicate that increasing the breaker concentration can reduce proppant-pack permeability damage very effectively.

Corrosion performance of welded CRA-lined pipes for flowlines

Abstract: This paper presents the results of corrosion and mechanical testing of welded high-nickel, corrosion-resistant-alloy (CRA)- lined pipes manufactured using various lining processes. The corrosion resistance of CRA-lined pipes for use as a flowline material in sour service was evaluated. The effects of the manufacturing process, CRA lining material, and welding on the corrosion performance of CRA-lined pipes also were determined

New Caustic Process for Softening Produced Water for Steam Generation

Abstract: Oilfield produced water containing a high concentration of total dissolved solids (TDS) and hardness can successfully be softened for use as oilfield steam-generator feedwater. At the Belridge in Kern County, CA, the combination of caustic softening and weak-acid cation exchange has been used to soften produced water containing 11,000 TDS and 550-ppm hardness to <1-ppm hardness. The resultant sludge containing calcium carbonate and magnesium hydroxide is concentrated by centrifuging and is disposed of in a landfill. Compared to the use of conventional strong-acid ion exchange followed by weak acid or weak acid followed by weak-acid ion exchange systems, the process offers the benefits of lower capital and chemical costs, partial silica removal, and elimination of liquid waste discharge

Completion techniques for horizontal wells in the Pearsall Austin Chalk

Abstract: Oryx Energy Co. used three basic completion techniques and various combinations of them to complete 20 horizontal wells in the Pearsall Austin Chalk. The completion method selected is based on a general set of guidelines. Additionally, equipment selection and various types of workover operations are reviewed

Use of low-shear pumps and hydrocyclones for improved performance in the cleanup of low-pressure water

Abstract: Although the advantages of using hydrocyclones for oily water cleanup are well proven, their use has been limited to applications where adequate system feed pressure for satisfactory operation was present. To use hydrocyclones in low-pressure operations, research testing was undertaken to determine the most suitable pumping system. Successful field trials with a low-shear progressive cavity pump and a single-liner hydrocyclone were conducted in the U.S. These trials provided the basis for full-scale tests on the Hutton platform in the U.K. sector of the North Sea. These tests demonstrated the feasibility of using large, low-shear, progressive cavity pumps in conjunction with multitude hydrocyclone units

Scale Prediction and Laboratory Evaluation of BaSO4 Scale Inhibitors for Seawater Flood in a High-Barium Environment

Abstract: The potential for scale formation after seawater injection must be carefully studied when a new oil field is being developed in order to provide proper input data for the basic engineering design. This paper presents the results of a study of several facets of scale occurrence and control for a developing North Sea field characterized by a high-salinity, high-barium (up to 1,000 ppm) formation brine. The results justify consideration of new technologies, such as treatment of the seawater to reduce the sulfate content.

Stabilization of montmorillonite clay in porous media by high-molecular-weight polymers

Abstract: A dynamic method is proposed for checking the stability of clay in porous media for different brine conditions and the stabilizing effect provided by several anionic and nonionic high-molecular-weight polymers. The method consists of injecting brine at decreasing salinity levels into clayey sandpacks until unstabilized permeability reduction is reached from the dislodging of clay particles that become trapped in pore restrictions. The last stable state before clay destabilization is characterized by a critical salinity concentration (CSC). As expected, montmorillonite clay 5% dispersed in a sandpack is more stable in the presence of KCl than NaCl brines, giving CSC values of 5,000 and 27,500 ppm, respectively

Flow Characteristics of Hydraulic Fracture Proppants Subjected to Repeated Production Cycles

Abstract: When fracture proppants are subjected to cyclic loading, the conductivity of the fracture is reduced This paper presents laboratory results to quantify the degradation of sand and intermediate-strength proppants (ISP's) as closure stress is loaded cyclically to the proppant The results imply that, if a deep gas well is opened and then shut in repeatedly, permanent damage to the hydraulic fracture will occur

CO2 -Foam Fracturing With Methanol Successfully Stimulates Canyon Gas Sand

Abstract: Successful stimulation using CO{sub 2} foam with methanol has revived the economically marginal Canyon gas-sand reservoir of Sterling County, TX. Field experience in the Conger (Penn) field demonstrated that CO{sub 2} foam (1) lessened the water required in the fluid and (2) provided a gas assist to help remove water and lower interfacial tension (IFT). The low pH of the fluid, combined with additional clay stabilization, iron control, and enhanced water recovery additives, proved helpful in initial well response and subsequent performances. Since the CO{sub 2}-foam fracture treatments were administered, production from Sterling County Canyon gas sands met or surpassed initial rates, even though formation pressure in the field declined 33.2%. Stimulation is essential for commercial production in these sands. However, water blockage, caused by stimulation, was encountered in designing an effective completion technique for a tight formation with reduced bottomhole pressure (HBP). Production in tight, low-pressure gas wells can be completely blocked if formation pressure does not exceed the capillary pressure increase caused by injected fracture fluid. Original stimulation techniques consisted mainly of gelled-water fracture treatments containing 65,000 lbm of 20/40-mesh sand with a maximum concentration of 2 1/2 lbm/gal. In many cases, several weeks of swabbing were requiredmore » to ensure continuous flow. After the fracture treatments, about 40% water recovery was realized throughout the field. This paper discusses CO{sub 2}-foam fracture treatments and job design and presents case histories from several Conger (Penn) field CO{sub 2}-foam fracture treatments.« less

Numerical simulation of gravel packing

Abstract: To obtain maximum productivity from unconsolidated formations where sand control is required, it is important to understand the mechanics of gravel packing. This paper describes a finite-element, numerical simulator that can predict gravel placement in the perforations and annulus of a wellbore. The equations for the simulator include mass and momentum conservation. Wellbore geometry, physical properties, and fluid and gravel-pack properties are simulator input. Experiments in a 100-ft full-scale wellbore model for three gravel-packing configurations have been successfully simulated. These configurations are a circulating pack with a washpipe, a squeeze pack, and a circulating/squeeze pack with a washpipe and a lower telltale screen. The low cost, speed, and extrapolation capabilities of the numerical simulator will greatly enhance our ability to predict gravel placement in a wellbore.

A new system for controlling the crosslinking rate of borate fracturing fluids

Abstract: This paper describes a delayed-crosslink activator system for borate fracturing fluids that allows crosslinking rates to be controlled to give low friction pressure in the wellbore. Data from laboratory development, full-scale friction test, and fracturing treatments are included to illustrate the fluid properties and the ability to couple fluid performance with treatment design. Field case histories include friction-pressure data, which profile the changes that occur as the fluid is crosslinking at different stages in the tubing. Results indicate that different crosslinking rates can be recognized by their friction-pressure signature and that the crosslinking rate can be altered easily during a treatment to minimize total treating pressure. This technique, with its resulting friction pressure profile, has proved to be an extremely useful tool for field optimization of crosslink times.

Optimal Fracture Stimulation of a Moderate-Permeability Reservoir - Kuparuk River Unit, Alaska

Abstract: Sixty-five percent of the reserves of the Kuparuk River field, the second-largest producing oil field in the US, is contained in a 20- to 80-md-permeability sandstone This paper provides details of stimulation design advances made over the past 3 years in this formation The design steps for optimizing fracture treatments in a moderate-permeability formation require primary emphasis on fracture conductivity rather than on treatment size or fracture length This philosophy was used for the 140 new wells documented in this paper Treatment size was gradually increased once a commensurate increase in fracture conductivity was obtained Applying the new design to the refracturing of 88 producing wells in the field resulted in an incremental 40,000 BOPD, a significant portion of the field's 300,000 BOPD

Diagnosis and Evaluation of Fracturing Treatments

Abstract: This paper introduced the pressure derivative in fracturing-pressure analysis. The derivative is shown to enhance the analysis capabilities significantly. The interpretation methodology is presented, and several field data sets and simulations are discussed to illustrate the technique