bluuebunny/crossref_metadata_2025 huggingface dataset:
Utilization of Density Logs to Delineate Desaturated Zones and Estimate Porosity in Cased Holes
Authors: Bishop J.M.
Published: December 2007

Density and neutron logs have been used in combination to both define and discriminate between desaturated and low porosity zones in cased holes at Coalinga and Mount Poso fields. Preliminary results further indicate that Preliminary results further indicate that cased hole density log readings can be used to estimate open-hole density log readings when favorable casing - cement - hole size condition exist. This technique should have utility in evaluating old wells where porosity control is presently not available and in providing the presently not available and in providing the option to run the formation density log after casing is set when well conditions preclude running the log in the open hole.

Introduction

Many shallow oil fields in the San Joaquin Valley of California are plagued with extensive reservoir liquid desaturation caused by gravity drainage and/or reservoir cementation. Since both conditions have a profound effect on the planning and ultimate success of supplemental planning and ultimate success of supplemental recovery projects, a considerable amount of engineering effort has been expended to determine the location and degree of reservoir desaturation and cementation.

Knowledge concerning the location and extent A desaturated and cemented zones is generally available on only the relatively few wells which have been recently drilled and logged with both resistivity and porosity devices. This unfortunate state of affairs has occurred because: 1. Many wells were drilled before the advent of wireline logging, 2. Many logged wells have only a resistivity record, which alone cannot be used to discriminate between desaturated and cemented zones, and 3. Much of the desaturation occurred after the drilling of the majority of the wells.

Many fields have been, or are nearly, fully developed; thus information concerning desaturation and cementation must be derived from the existing cased holes. Cased-hole gamma ray-neutron logs can be successfully used to define sands and shales and to locate porous, liquid-filled zones. However, the neutron log cannot, in general, discriminate between liquid-filled zones of decreasing porosity and porous zones that are desaturated to varying degrees. The problem of discriminating between such zones is problem of discriminating between such zones is solved in the open hole by running a neutron log with either the sonic or density log and crossplotting the apparent log porosities. No such technique has been previously available in cased holes.

The density log was developed and has been utilized strictly as an open-hole logging device.
The Effect of Temperature on Water - Oil Imbibition Relative Permeability
Authors: Ehrlich Robert
Published: December 2007

Silica or limestone porous materials in contact with pure hydrocarbon liquids are strongly hydrophilic. When naturally occurring surface active materials are present in the liquid, they are adsorbed at the solid surface, rendering it less hydrophilic. If the concentration of such material is sufficient, the oil-water-matrix contact angle can be significantly greater than zero. The effect of increasing temperature in such a system will usually be to shift the adsorption equilibrium causing desorption of surface active material and a decrease in contact angle.

A simple geometrical model of a porous medium is used to approximate the effect of variation in wettability, as characterized by the oil-water-matrix contact angle, on imbibition relative permeability. Based on this model and other considerations, we conclude that the following trends will occur in a series of isothermal water floods with temperature increasing;

oil-water-matrix contact angle decreases to zero; residual oil saturation decreases; the ratio krw/kro at a fixed water saturation can increase for materials with a low residual oil saturation such as unconsolidated sands; the ratio krw/kro at a fixed water saturation decreases for materials with a high residual oil saturation such as consolidated sands.

Experimental observations of these conclusions are reported in the literature.

A method is presented for the correction of imbibition relative permeability curves to compensate for changes in temperature, based on the model developed.
Case Histories Of Carbonated Waterfloods In Dewey-Bartlesville Field
Authors: Hickok C.W. , Ramsay H.J.
Published: December 2007

Commercial carbonated waterfloods (Orcofloods) are being carried out in Oklahoma, Texas, and Kansas. Three of these unique floods were initiated in the Dewey-Bartlesville Field, Washington County, Northeast Oklahoma.

The carbonated floods are surrounded by conventional waterfloods in the same reservoir, thus making possible a direct comparison of ultimate oil recovery, water injectivity, and flood life. Increased oil recovery, increased water injectivity, and shorter flood life are economically benefits obtained from the carbonated floods.

Two of these carbonated waterfloods (initiated in 1958) are now almost depleted, thus enabling predictions of ultimate oil recovery. And for comparison, conventional waterfloods (initiated in 1953) which are immediately South and West of the carbonated floods, have progressed to the point where ultimate oil recovery also can be estimated.
Analysis and Prediction of Gas Well Performance
Authors: Coats K.H. , Dempsey J.R. , Ancell K.L. , Gibbs D.E.
Published: December 2007

This paper describes a numerical model for analyzing gas-well tests and predicting long-term deliverability. Field applications presented include an interpretation of a gas well test in a tight sand leading to an accurate long-term deliverability projection. The model presented numerically simulates two-dimensional (r-z) gas flow and accounts for effects of turbulence, skin, afterflow, partial penetration, pressure-dependent permeability and pressure-dependent permeability and any degree of crossflow ranging from complete to none. Through a novel treatment of the equations describing reservoir flow, skin and afterflow, the model simulates shutin at the wellhead and then calculates afterflow and any subsequent circulation of gas through the wellbore from some layers to others.

Introduction

Many gas wells exhibit pressure test behavior which is difficult if not impossible to interpret using conventional methods of analysis. Difficulty of interpretation is frequently encountered in low permeability reservoirs and in layered reservoirs with limited or incomplete crossflow. In these cases, assumptions in conventional analysis methods, such as complete (or no) crossflow and negligible effects of afterflow or interlayer recirculation through the wellbore, are frequently invalid.

This paper describes a numerical model which accounts for many factors which are neglected in conventional methods of analysis. The model numerically simulates two-dimensional (r-z), transient gas flow in a cylinder representing the drainage volume of a single well.
How to Evaluate and Select Premium Casing Connectors
Authors: Jellison Michael J. , Davila Manuel Alfredo
Published: December 2007

Selecting the appropriate connector for each casing string in a well represents a difficult challenge for drilling engineers. The engineer must decide if an application requires a premium connector or can be satisfied with an API connector. If use of a premium connector is dictated by the well conditions the large number of premium connectors available further complicates the decision of which connector to use.

This paper provides guidelines on how to evaluate and select premium connectors for drilling and production casing, tieback and liner applications. In addition, guidelines to assist in determining when a premium connector is required over an API connector are presented.
The Principles and Procedures of Geosteering
Authors: Lesso W. G. , Kashikar S. V.
Published: December 2007

The management of directionally drilled wells has recently progressed to the stage where targets have been reduced in size to a point in the earth with no tolerances. These targets can and are changed during the drilling process. The management of these point moving targets, usually in high angle or horizontal wells, is a precise form of directional drilling now called geosteering. It is this precise placement of the wellbore that creates the value in drilling these wells.

Several technologies have made this advancement possible. These include reliable steerable systems, improved and new physical formation measurements, log data modeling, sensors near the bit and instrumented motors, and detailed reservoir mapping with the help of 3D seismic processing. Most papers on geosteering have concentrated on one of these advances. This paper addresses how these technologies are merged to execute the successful geosteering project.

New systems, sensors, and computations have created a mass of data and control parameters that require real-time decisions bv operator personnel based on technical recommendations from service companies. These decisions have a critical impact on the net worth of a project. The team involved must rely on each other's expertise and understand the overall objective of a geosteering project. To do this, it is paramount that data from these different technological areas be merged into a 3D visualization encompassing geological structures and drilling trajectories.

Patterns in procedures have developed from these projects over the past three years which demonstrate the difference between a successful project and a failure. The examples in this paper illustrate the techniques that will enable a change in the outlook towards precision directional drilling and completion projects.
Multi Operator Programme for Deep Water Drilling
Authors: Talbot J. R. A. S.
Published: December 2007

During the last ten years, the majority of offshore exploration drilling contracts have been of short term duration with Operators able to pick up Mobile Offshore Drilling Units (MODUs) relatively easily and lay off the term risk onto the Drilling Contractors. At present, demand for deep water dynamically positioned drillships (D.P.D.S.s) and semi-submersibles exceeds supply and this trend is widely predicted to continue over the medium term.

This paper is offered as a framework to help promote the sharing of drilling assets by the Operators to the advantage of both Operators and Drilling Contractors alike. Drilling Contractors require long-term work schedules at reasonable rates to justify their investments – Operators in today's offshore market need to be able to access MODUs to effect their licence obligations and appraise new discoveries sufficiently prior to approving investments.
Hole Cleaning Modelling: What's ‘n’ Got to Do With It?
Authors: Kenny Patrick , Sunde Egil , Hemphill Terry
Published: December 2007

Efficient hole cleaning is vitally important in the drilling of directional and extended-reach (ERD) wells. In previous works, the importance of fluid velocity/pump output has been emphasised, while in others, the importance of individual fluid rheological parameters has been stressed. Drillpipe eccentricity and rotation directly affect hole cleaning as well. Recent work on particle settling velocity has accelerated the understanding of the behaviour of drilled cuttings in wellbores.

This paper presents a new model to the industry, which combines recent developments in the fields of particle settling and rheology. This model provides a useful tool for the planning of hole cleaning for highly deviated wells through the use of Lift Factors under the eccentric drillpipe. Information from deviated wells in the field is used to illustrate the usefulness of this hole cleaning model. Importantly, analysis of the data indicates that fluid ‘n’ factors calculated using the yield-power law [Herschel-Bulkley] rheological model play a greater role in promoting good hole cleaning in ERD wells than has previously been recognised.
Mechanisms of Differential Sticking and a Simple Well Site Test for Monitoring and Optimizing Drilling Mud Properties
Authors: Reid P. I. , Meeten G. H. , Way P. W. , Clark P. , Chambers B. D. , Gilmour A.
Published: December 2007

Differential sticking has a major impact on drilling efficiency and well costs. Although some problems can be related to the characteristics of rock formations, or to drilling parameters not related to drilling mud properties, it is widely accepted that the mud formulation and condition strongly influences the risk and severity of differential sticking incidents.

In this paper we use our own laboratory data and information from industry publications to formulate the mechanisms of differential sticking and the key drilling mud parameters that can influence the process. Using this knowledge, we have built a simple and robust device for measuring the sticking properties of muds in the laboratory or at the well-site. This device comprises a half area HTHP fluid loss cell which is modified to allow a metal sphere to be placed in contact with a growing mud filtercake. The torque required to rotate the sphere free from the mud cake is determined using an electronic torque gauge. We find that a plot of torque against the 3/4 power of time (this power term derives from the build-up of cake around a spherical object) gives a linear fit to the data, and that the slope of this line is indicative of the sticking potential of the mud. An extensive analysis of laboratory-mixed and field muds indicates that the test gives a good indication of mud condition and allows the user to investigate various options for reducing the sticking potential of the fluid. This information is useful both in the initial selection of mud type and in making technical and economic analyses of various mud treatment options.

In addition to the laboratory evaluation described above, the sticking device has been used in several wellsite tests with encouraging results. Some of these are described.
How to Improve Rate of Penetration in Field Operations
Authors: Fear M. J.
Published: December 2007

A method has been developed that identifies which factors are controlling rate of penetration (ROP) in a particular group of bit runs. The method uses foot-based mud logging data, geological information, and drill bit characteristics, to produce numerical correlations between ROP and applied drilling parameters or other attributes of drilling conditions. These correlations are then used to generate recommendations for maximising ROP in drilling operations.
Safety By Design as Applied to the Design and Fabrication of Rig 200
Authors: Hubler Warren G. , Roberts H. D.
Published: December 2007

The foundation for safety of any operation is determined long before people, procedures and equipment come together to provide a service or produce a product. It is determined during design and construction. This paper begins by outlining the systems safety approach to minimizing hazards and integrating safety into the design and engineering of an operation (Part I). It describes methods for identifying, analyzing and eliminating workplace hazards. Part II of the paper describes the application of systems safety tools to the design and fabrication of a new construction, highly mechanized, platform drilling rig. Implementation of the systems safety approach impacts directly on safe, productive and cost effective operations.
Field Examples of Gas Migration Rates
Authors: Grace R. D. , Shursen J. L.
Published: December 2007

In recent years gas migration rates have become the center of considerable controversy. Historically, field personnel have used a "rule of thumb" that gas migrated at the rate of 1000 feet per hour. Early basic research1 illustrated that the factors affecting the rate of bubble rise were quite complex. For example, the rate of rise was affected by the properties of the influx, mud properties, the eccentricity of the hole, and the size of the annulus, to name a few.

The rate of rise was also affected by the manner in which the influx entered the wellbore. If the influx was dispersed in the mud as small bubbles, the rise characteristics were different than if the influx entered the wellbore as a continuous bubble. A dispersed influx generally migrated much slower than a continuous bubble.

It was generally expected and observed that as an influx began to migrate toward the surface, the surface pressure would begin to increase. The incremental changes in surface pressure were utilized to determine the rate of rise and predict the travel of the influx. In addition, these techniques were used to model the well control problem, expand the influx, protect the casing shoe, and otherwise analyze the problem. However, in many instances, the variables were too complex to permit accurate calculations and analyses in field operations and the old rules of thumb were utilized.
A Direct Approach for History Matching
Authors: Veatch R.W. , Thomas G.W.
Published: December 2007

Introduction

Mathematical reservoir simulation models are widely used to predict field behavior. Their use requires that permeability and porosity be specified at numerous points throughout the reservoir. The usual procedure is to first estimate these parameters, compute the past field history and then compare the computed results with the observed performance. If the comparison is not satisfactory, the estimates are repeatedly modified until an acceptable match is obtained. It is then assumed that the rock properties are adequately specified for future predictions.

This trial and error procedure can consume considerable computer time and money. In view of this, some people have investigated iterative adjustment and regression techniques linear and nonlinear programming methods and energy dissipation analysis in an effort to automate the procedure. These methods are essentially similar insofar as they are ex post facto techniques; i.e., after one or more computer runs have been executed, then the known performance history is used in some fashion to performance history is used in some fashion to deduce an acceptable set of rock parameters. This approach is tantamount to using a differential equation solver for treating an inverse problem, and is not the most efficient.

In this work, we present a direct method for treating the inverse reservoir simulation problem. The technique enables one to compute problem. The technique enables one to compute reservoir permeabilities and porosities in a single computer run utilizing appropriate data from several periods of the performance history. It is applicable to multiphase, compressible flow in heterogeneous reservoirs. A procedure is described that recognizes, during the course of the computation, whether or not a unique solution can be obtained. The method is capable of handling inconsistent data and constructing the best set of non-unique properties within realistic limits when unique solutions do not exist.

Results of studies on several hypothetical reservoir problems are presented. Finally, examples which show the effect of non-unique history matches on future predictions are also cited.
Mathematical Modeling of Gravity Drainage After Gas Injection into Fractured Reservoirs
Authors: Schechter D. S. , Guo B.
Published: December 2007

This paper addresses mathematical modeling of free-fall gravity drainage which is believed to occur in naturally fractured reservoirs after depletion of oil in the fractures or gas injection into the fractured system. Comparison of wetting phase recoveries calculated using existing math-ematical models with experimental data indicates the in-accuracy of these models. The causes of error are identified to be the unrealistic assumptions made in formulation of the models. Based on Darcy's law and film flow theory, we have developed a new mathematical model to describe the free-fall gravity drainage process, A simple non-linear governing equation for phase demarcator in dimensionless form was formulated and solved numerically as a function of dimensionless time. Based on the dimensionless demarcator, fluid recovery during free-fall gravity drainage is calculated. Comparisons of wetting phase recoveries given by the new model with 20 sets of experimental data obtained under thermodynamic equilibrium conditions for a variety of fluids and cores show much better accuracy of the model over the existing models. Using the dimensionless time, tD — ke∆𝜌gt/𝜇L, fluid recovery obtained from laboratory studies can be scaled to field applications for estimation of projected oil recoveries in oil fields. We have also applied the new model to simulation of free-fall gravity drainage under non-equilibrium conditions where molecular diffusion between phases is considered. Experimental oil recovery data obtained from CO2 injection into a Berea core and a reservoir sandstone core, which were saturated with separator oil, have been matched by the model using empirical correlations for fluid properties. The objective of this paper is to provide reservoir engineers with a useful tool for estimating the oil recovery from fractured reservoirs after gas injection.
The Application of Hydraulic Fracturing Models to Characterize Fracture Treatments in the Brushy Canyon Formation, Delaware Group, Eddy County, New Mexico
Authors: Johnson Raymond L.
Published: December 2007

In this study of the Brushy Canyon, sonic-derived, rock-mechanical properties and bottomhole treating pressure (BHTP) data from mini and main fracture treatments will be history-matched with three-dimensional (3D), lumped 3D, and pseudo 3D fracture models. Height dimensions obtained from these history-matches are compared with temperature and radioactive tracer surveys to better characterize fracturing mechanics in this Delaware Mountain Group formation.
A New Approach to Large-Scale Infill Evaluations Applied to the OZONA (Canyon) Gas Sands
Authors: Voneiff G.W. , Cipolla Craig
Published: December 2007

Historic "sweet spots", areas of well-to-well interference, and infill potential were determined for an 1800 well area of the OZONA (Canyon) field using a new approach that focuses on the age of the wells, their location, and production profiles. At the core of this new approach, termed "moving domain", is a mosaic of automated studies that draw statistical conclusions about well performance, depletion, and undrained acreage. Preliminary infill estimates in one to two weeks are possible and the technique is typically linked to conventional reservoir engineering to improve estimates. When applied to OZONA (Canyon), 1246 infill locations were identified with 636 Bcf of gas reserves.

Introduction

History - The OZONA field, located in Crockett County in Southwest Texas (Figure 1) contains two major producing sands, the Canyon and the Penn. These sands are complex turbidite deposits that are characterized by numerous gas productive members with permeabilities from less than 0.001 mD to over 0.10 mD and are found at depths of 6,000 to 8,000 ft.1 A recent change in field rules will allow drilling to 40 acres spacing in most parts of the field. Initial development began in the early 1960s on 320 acre spacing, with subsequent infill drilling on 160- and 80 acre spacing. Typical completions require fracture treatments using water based fluids containing 50 to 250 klbs of 20/40 sand to achieve economic production rates. Ultimate gas recoveries range from 200 MMCF to over 2000 MMCF and can vary significantly from well to well. Historically, many wells with multiple pay zones were fracture treated simultaneously, while other wells were fracture treated in isolated stages.

Problem - Quantifying the infill potential in the OZONA (Canyon) field is difficult for several reasons: the layered and low permeability nature of the reservoir, the hydraulic fracturing of wells, the variation in well spacing, and the local and regional variations in rock quality. These complicating factors often cloud the extent of depletion, benefits of improved completion and operation techniques, and make the quantification of infill potential rather difficult. Because of these complexities and the fact that our study area contained over 1000 wells, the time and cost requirements of a conventional reservoir engineering study were unacceptable. Instead we applied a new technique that was found to be useful in a large tight gas field in East Texas.2
Improved Water Flood Operation in the Permian Basin Through Microbial Culture Treatment
Authors: Ratliff T. , Hoskins B. C. , Schneider D. R.
Published: December 2007

Microbial cultures can be used to reduce or eliminate scale formation in water flood injection systems. Several water floods have been treated for over a year with microbial culture products and the effects of the treatment on operating performance has been studied. The injection systems initially showed significant scale problems from calcium sulfate and calcium carbonate. Tracking water flood performance parameters such as injection pressures and volumes over the treatment period showed that, as compared with prior treatment historical data, a variety of positive results of treatment were evident. For example, the flood injection volumes were stabilized or increased, injection pressures were stabilized and oil and gas production was increased. Laboratory studies of injection water showed that filtration times could be significantly reduced by microbial treatment, indicating that near well-bore occlusion could be reduced by such treatments. The microbial treatments were considered more effective than prior alternative treatment technologies. This new technology offers a cost-effective superior alternative to conventional technologies.
Review of Downhole Dynamometer Testing
Authors: Soza Roberto L.
Published: December 2007

Electronic Downhole Load Cells (DHLC) have been used to quantify rod loadings calculated by predictive and diagnostic wave equation programs. Test results to date show that software calculations agree closely with DHLC measurements. However, there is a difference in how software programs account for buoyant forces which results in discrepancies in reported loads and placement of the zero load line. The overall impact of this difference in the tests run to date, has not been large and may only be critical in the most demanding rod pumping conditions.
CO2 Huff-n-Puff: Initial Results from a Waterflood SSC Reservoir
Authors: Wehner S. C. , Prieditis J.
Published: December 2007

The application of cyclic CO2, often referred to as the CO2 Huff-n-Puff (H-n-P) process, may find its niche in the maturing waterfloods of the Permian Basin. Coupling the CO2 H-n-P process to miscible flooding applications could provide the needed revenue to sufficiently mitigate near-term negative cash flow concerns in these capital intensive projects. Initial results from a field demonstration of the process are provided. The paper briefly reviews the reservoir characterization associated with the project and the compositional simulation of the CO2 H-n-P process. Simulation results suggest that reservoir characterization of flow units is not as critical for a CO2 H-n-P process as for a miscible flood. Entrapment of CO2 by gas hysteresis is considered the dominant recover» factor for a given volume of CO2. The repetitive application of the process was found to be unwarranted in a waterflooded environment. Future history matching of the performance will allow better forecasts and evaluation of the economic impact available with this underutilized process.
Reduced Costs Propel Shallow Gas Program in Southeast New Mexico
Authors: Bounds C. M. , Brown E. K.
Published: December 2007

A significant reduction of drilling and completion costs in the Eumont and Jalmat Fields of Lea County, New Mexico has resulted in the continuation of Conoco's development program in a soft gas price environment. Average 1995 costs for drilling, completion and facilities have been reduced to $180,000 for single zone completion wells and $240,000 for two completion wells. This paper focuses on the process and equipment changes that resulted in the cost improvements as well as the method used to identify the improvements.
An Evaluation of Gas Field Rules In Light of Current Conditions and Production Practices In the Panhandle Non-Associated Gas Fields
Authors: Brady C. L. , O’Rear C. H.
Published: December 2007

During the early years of development in the Panhandle fields the Rule of Capture was king. Under the Rule of Capture each property owner has the right to drill as many wells as desired at any location. Adjacent property owners protect their rights by doing the same. Courts adopted the Rule of Capture to protect mineral owners from liability due to migration of oil and gas across property boundary lines. This general practice "to go and do likewise" generally leads to enormous economic and natural resource waste.

Established to offset the waste created under the Rule of Capture is the doctrine of Correlative Rights. Correlative Rights is the right of each mineral owner to obtain oil and gas from a common source of supply under lawful operations conducted from his property. However, each mineral owner has a duty to every other mineral owner not to extract oil and gas in a manner injurious to the common source of supply.

This paper will examine the historical context of these common law principles with regard to the Panhandle non-associated gas fields. Discovered in 1917, the Panhandle fields are ideal to evaluate the merit of statutes and regulations enacted in response to production practices. As in many Texas fields, proration in the Panhandle fields is the primary mechanism to protect correlative rights and prevent waste. Signed and made effective May 1989, the current field rules pre-date much of the enhanced recovery techniques that use well-head vacuum compression. This paper reviews the gas rules in the 1989 Texas Railroad

Commission order in light of current reservoir conditions and production practices.
Potential Distribution Around Sources With Finite Length Horizontal, Vertical Partially Penetrating Wells and Fractures Part II: Transient Flow
Authors: Azar-Nejad F. , Tortike W. S. , Farouq Ali S. M.
Published: December 2007

The potential distribution around a partially penetrating source is a solution of the diffusivity equation. Presenting a new method "Discrete Flux Element" (DFE) this paper provides the solution to the diffusivity equation with uniform potential as well as uniform flux inner boundary conditions (IBC). This solution provides the ability for modeling any sources with arbitrary geometry. The pressure derivative equations have been derived for uniform potential as well as uniform flux inner boundary conditions. The pressure derivative reflects the wellbore length and the distance of a horizontal well to the no-flow boundary.
Conversion of a Semisubmersible Drilling Rig to a DP Unit
Authors: Vale Edson L. Megale , de Medeiros Edmilson S. , Neto Arthur C. , Ferreira Paulo P. Ribas
Published: December 2007

The scopc of work which this paper is based on is the conversion of the semisubmersible drilling rig PETROBRAS-XXIII (Ex-VINNI) from the original mode of operation to a dynamic positioning unit, capable to operate on offshore fields of Brazilian coast from 100 to 1500 m water depths.

Originally such unit was designed by GVA, named GVA 4000, to operate up to 460 m water depth, positioned by means of a 8-point mooring system.

The conversion is based on the brazilian waters environmental conditions and the design criteria is according to DNV rules and the principle of NMD, as stated for class 2.
Controlling Water Production In Naturally Fractured Reservoirs With Inorganic Gel
Authors: Fragachán F. E. , Cázares-Robles F. , Gutiérrez J. J. , Herrera G.
Published: December 2007

This paper presents the results of successful applications of inorganic gels to control water production. In naturally fractured reservoirs a case study with hostile high temperatures (260-310 °F) found in the Cretaceous and Jurassic dolomitic limestone's of the south east of Mexico is presented together with a water exclusion case from the tertiary sandstones. Importance of gel penetration and selective placement to considerably delay the water percolation to upper intervals in hydraulically communicated intervals is discussed. Included are alternatives for control of gel invasion from the high conductivity fracture network to the tight matrix. Finally, the paper presents a brief discussion of the future of water control in naturally fractured reservoirs.
Design and Analysis of Fractured Horizontal Wells in Gas Reservoirs
Authors: Soliman M. Y. , Azari M. , Hunt J. L. , Chen C. C.
Published: December 2007

Although horizontal wells may offer significant production improvement over vertical wells, it may be necessary to fracture horizontal wells to maximize their return on investment. This is especially true in the case of tight gas formations.

This paper presents a model for fractured horizontal wells operating under constant pressure conditions, which is most suitable for producing tight gas reservoirs. The created fracture may be longitudinal or transverse. In this paper we examine the factors involved in determining the optimum number of transverse fractures for both finite and infinite reservoirs. For a group of transverse fractures, the rate distribution for each fracture is presented and analyzed. The effect of uneven fracture length is briefly presented.

The performance of a longitudinal fracture is examined and compared to a fractured vertical well and to a transverse-fractured horizontal well. A comparison of longitudinal versus transverse fractures from reservoir and operational points-of-view is presented. Also included is a short discussion of field examples.

Because performance of a longitudinal fracture is almost identical to that of a fractured vertical well, the existing solutions for fractured vertical wells may be applied to longitudinal fractures with a high degree of confidence. This approximation is valid for moderate to high dimensionless conductivity. In the case of transverse fractures, the outerfractures outperform the inner fractures. However, more than two fractures are necessary to efficiently produce the reservoir for most cases. A simplified economical analysis supports this conclusion.
Applications of Simulated Annealing on Actual but Atypical Permeability Data
Authors: Savioli G. B. , Falcigno E. D. , Bidner M. S. , Lake L. W.
Published: December 2007

The use of geostatistics is becoming recognized as a standard means of representing reservoir heterogeneity, Geostatistics has enjoyed an extensive use and a fairly well developed theoretical base. This is a little less true of simulated annealing (SA), the form of geostatistics tested here, but it is also a mature technology.

Yet there remains a need to exercise these procedures under actual conditions of nonuniformly sampled data, non-Gaussian distributions and truncated data sets. Providing insights into how to deal with these nonidealities is the objective of this work,

We find that SA estimates are improved when the original data sets are power-transformed. However, SA estimates tend to deviate from the input cumulative distribution function (CDF) because of excessive rejections. This deviation can be corrected by including the CDF into the SA objective function.
Biological Water Profile Control - Designing a Concept for North Sea Application
Authors: Paulsen John E. , Sørheim Roald
Published: December 2007

Water profile control, using indigenous nitrate reducing seawater bacteria in North Sea waters as blocking agents, has been investigated. Feasibility studies have been carried out, both in a micro (micromodels) and a meso scale (sand packs), aiming at identifying parameters that are critical for the process. The results show that there are several factors that are important for the penetration and distribution of a bioplug in a porous matrix. Although lab experiments have shown that bacteria preferentially block high permeable zones, it is questioned how relevant this information is for practical purposes. The long distances involved in transport of bacteria and nutrients into North Sea reservoirs implies problems that have to be resolved. Biofilms growing as a network in pores in the matrix, biowebs, are proposed to play a major role in the development of a bioplug. The filterability of the matrix is increased once the bioweb is established, and entrainment of fines and bacteria is dramatically impeded. pH alterations, due to acidic metabolic by-products, is believed to be rate limiting for the generation of biomass in the porous matrix. This problem, in conjunction with the problem created by the biowebs, is speculated to be main obstacles in a plugging scheme in large fields with distant target zones. The problem of scale seem to be extremely important. It is questioned if the current methodological approach in the study of biofilms is adequate for studying phenomena that aredistant in,time, and space.
Gel Systems for Controlling CO2 Mobility in Carbon Dioxide Miscible Flooding
Authors: Raje M. , Asghari K. , Vossoughi S. , Green D. W. , Willhite G. P.
Published: December 2007

Carbon dioxide miscible flooding is widely used in carbonate reservoirs in West Texas and has potential application to carbonate reservoirs in other areas of the country including Oklahoma, central, and southwest Kansas. One of the major difficulties of this process is the CO2 early breakthrough because of its unfavorable mobility ratio and because of the heterogeneous nature of this type of reservoir. Injection of alternating slugs of water and carbon dioxide, known as the WAG process, is the remedy most widely applied to control the early breakthrough, but its success has not been universal. Conformance control using gels has not been widely attempted. Laboratory research efforts at the University of Kansas have produced promising in situ gelation techniques aimed at this application.

Three in situ gel systems have been developed and tested in laboratory cores to control the movement of supercritical CO2 in matrix rock. Two systems are based on a new biopolymer, termed KUSP1, which is soluble in alkaline solutions above pH 10.8, but forms firm gels when the pH is reduced to 10.8 or below. The third gel system uses the reaction of sulfomethylated resorcinol and formaldehyde to form a gel. This paper describes the behavior of these gel systems at 32.2-41°C in Berea sandstone cores (initial permeability ~ 70 – 700 md) when exposed to supercritical carbon dioxide and brine after in situ gelation.

KUSP1 gel systems were studied using two different methods of inducing in situ gelation. In the first method, gelation was accomplished by injecting CO2 at low pressure into the Berea sandstone core saturated by alkaline polymer solution. Permeability reduction to the brine and CO2 in the range of 80% was achieved. Stability of the gel was tested in the presence of supercritical CO2. When supercritical CO2 was used to induce in situ gelation, the same degree of permeability reduction was achieved. The gel remained stable after the injection of many pore volumes of supercritical CO2. The second method of initiating in situ gelation involved the use of an ester. Hydrolysis of the ester, monoethylphthalate, in the alkaline polymer solution caused the pH to drop to levels where in situ gelation occurred. The permeability of the treated core to supercritical carbon dioxide was about 1 md which was equivalent to a permeability reduction of 95-97 % of the initial brine permeability.

The third gel system, based on the reaction of sulfomethylated resorcinol and formaldehyde, termed SMRF, was gelled in situ and contacted with both brine and supercritical CO2. Permeabilities to carbon dioxide on the order of 1 md or less were observed. This permeability is equivalent to a reduction of about 99% in the initial brine permeability. Reduced permeabilities were maintained after injecting many pore volumes of supercritical CO2 and brine.
Optimization of Miscible Water-Alternate-CO2 Injection (Based on analytical model)
Authors: Bedrikovetsky P. , Andrade G. M. , Ferreira L. E. A. , Menezes G. L.
Published: December 2007

A new analytical model for the miscible CO2-WAG is developed. The model is based on analytical solutions of non-self-similar and self-similar problems for system of hyperbolic equations of mass conservation laws. Explicit formulae allow to analyse propagation of displacement and phase transition fronts, mechanisms of trapping of oil with the sequential injection of water and gas slugs, mobility ratios on shock fronts and the dynamics of water and gas slugs.

Five different regimes for gas-water injection have been distinguished depending on the water-gas ratio. They differ from each other by different structure of the mixture zone and displacement mechanisms caused by phenomena of two-phase displacement and phase transitions.

The analytical model presented shows that the higher the WGR the lower the recovery, but the more favourable is the mobility ratio on the displacement front. These suggest the existence of an optimal water-gas ratio (WGR).

As it follows from the analytical model there does exist a minimum slug size which prevents gas breakthrough via all the water slugs. With the injection of thinner slugs a connected gas network appears in the reservoir which will catch up the front of water and will create an unstable gas-oil front at the presence of the connate water only. So, simultaneous injection of gas and water, which accords to the reduction of slug size to the zero limit, is not an optimal WAG regime, as it was suggested in the literature. On the other hand the thinner the slugs the higher the displacement efficiency. These speculations suggest the existence of an optimal slug size with the miscible WAG.
Permeability Damage in Diatomite Due to in-situ Silica Dissolution/Precipitation
Authors: Koh C. J. , Dagenais P. C. , Larson D. C. , Murer A. S.
Published: December 2007

It has been observed in Mobil’s California diatomite thermal recovery projects that water injectivity decreases gradually with time. Several factors, such as reservoir fill-up or high suspended solids concentration in the injection fluid, may effect such decrease. Due to the inherently low permeability of diatomite, small amounts of in-situ silica dissolution and/or precipitation can also have a drastic effect on the matrix permeability and consequently the injectivity. In this study, we outline an experimental program designed to ascertain such behavior and to elucidate qualitative and quantitative results to further our understanding of the problem. Furthermore, transient flow experiments were performed to obtain silica dissolution/precipitation data at various temperatures. It is shown that the silica reaction can be modeled approximately as first-order kinetics. Numerical model results indicate that this kinetic data can be used to model diatomite permeability damage data obtained in the laboratory. Our current effort to simulate field-scale permeability damage using the experimentally-derived silica kinetic model will also be discussed.
Improving CO2 Floods in Heterogeneous Media
Authors: Yaghoobi H. , Tsau J. S. , Heller J. P.
Published: December 2007

Selective mobility reduction (SMR)-enhanced foam reduces mobility of CO2 by a greater fraction in high than in low permeability cores in the laboratory experiments.1–4 The occurrence of such an exciting property has been verified several times experimentally with isolated core samples ranging from less than one to more than 900 millidarcies. However, the existence of SMR in composite, heterogeneous cores as well as the benefits of applying this unusual property in oil recovery have not been investigated. This paper addresses both the effect of foam on improving CO2 mobility in heterogeneous rocks, and also examines further the effect of heterogeneity on gas floods unprotected by surfactant.

To simulate experimentally the heterogeneous character of reservoir, composite cores which contain coaxial zones of high and low permeability in capillary contact are used in the latest experiments. The experiments are conducted in a high-pressure flow system that enables the flows to be segregated, with the brine and CO2 effluent from each of the zones collected and measured separately. The preliminary results indicate that the capillary contact between parallel zones does not diminish SMR. This interesting and striking finding clarifies the existence of SMR and its applicability in a real reservoir condition. As in previous single core tests, however, it is found that not all surfactants exhibit SMR to the same extent and that lower surfactant concentrations often provide a more intense SMR than do stronger solutions.

To model computationally both displacement and steady-state flow in a parallel-layered system with no foam, a DOE-distributed MASTER (Miscible Applied Simulation Techniques for Energy Recovery) reservoir simulator was used. The numerical results agreed qualitatively with those of the "control experiments" undertaken for comparison with the foam experiments performed in the same parallel system and reported earlier.5 These results were that the flow induced a saturation contrast between the parallel regions of different permeability. In the case of CO2 or other gas floods, this effect increases the high mobility ratio.
Reservoir Characterization by Integration of Seismic and Dynamic Data
Authors: Huang Xuri , Kelkar Mohan
Published: December 2007

This paper presents a systematic procedure for integrating 3D seismic data and production data to develop a detailed reservoir description. The procedure involves three steps. Step one includes the inversion of the seismic data to construct impedance distribution with the well core and log data. Step two includes the simulation of porosity values consistent with the impedance data. The last step involves the estimation of permeability values consistent with its relationship with porosity as well as the dynamic information. All these three steps are discussed in detail. The procedure is further validated by applying it to both synthetic and the field data. The results obtained have been satisfactory illustrating the suitability of the method.
Crossflow in Fractured/Layered Media Incorporating Gravity, Viscous, and Phase Behavior Effects: Part II - Features in Fractured Media
Authors: Dindoruk B. , Firoozabadi A.
Published: December 2007

Crossflow across the interfaces of layered reservoirs, and between matrix blocks and fractures in fractured reservoirs may be very pronounced.

In Part I of this study, the results of our work on crossflow in layered media were discussed. In this paper, the results for fractured porous media will be presented. Based on several example problems, we observe a significant contribution of crossflow to recovery performance in a fractured porous medium. In one example, the in-place hydrocarbon recoveries at 1 PV injection are 68 percent with crossflow between the matrix and fracture, and 47 percent without crossflow. Those results correspond to a single matrix block. The effect of crossflow in a multiblock system may be even more pronounced.

The results presented in this paper provide a real challenge for compositional simulation of fractured reservoirs.