Buildup Tests Research Articles

Explicit Deconvolution of Well Test Data Dominated by Wellbore Storage

This paper addresses some methods for interpretation of oil and gas well test data distorted by wellbore storage effects. Using these techniques, we can deconvolve pressure and rate data from drawdown and buildup tests dominated by wellbore storage. Some of these methods have the advantage of deconvolving the pressure data without rate measurement. The two important methods that are applied in this study are an explicit deconvolution method and a modification of material balance deconvolution method. In cases with no rate measurements, we use a blind deconvolution method to restore the pressure response free of wellbore storage effects. Our techniques detect the afterflow/unloading rate function with explicit deconvolution of the observed pressure data. The presented techniques can unveil the early time behavior of a reservoir system masked by wellbore storage effects and thus provide powerful tools to improve pressure transient test interpretation. Each method has been validated using both synthetic data and field cases and each method should be considered valid for practical applications.

The Severe Loss of Well Productivity in an Iranian Gas Condensate Carbonate Reservoir: Problem Identification and Remedy

Khami reservoir of Marun field is a gas condensate carbonate reservoir with initial pressure and temperature of 12,556 psia and 285°F, respectively, at a specified reference depth. The high pressure and high temperature condition along with carbonate lithology make this reservoir a matchless gas condensate reservoir worldwide. This article, as a field case study work, discusses a comprehensive work to identify the source of severe loss of productivity and find the best remedial technique for one of the wells in this reservoir. Pressure buildup test data were used and well test diagnostic, interpretation, and analysis was performed using pressure transient analysis software. Extreme buildup of condensate bank around the wellbore, due to bottomhole pressure below the dew point pressure, was observed. The buildup of condensate bank causes a composite reservoir behavior with two mobility zones, a high condensate saturation region followed by a region of gas with initial condensate saturation. Then, to analyze well inflow and outflow performance of production system, a multiphase flow simulator software was used. Deficiency and sensitivity of well inflow performance was concluded; therefore, effect of hydraulic fracturing on improving inflow performance and recovering well productivity was investigated. Considerable improvement in productivity could be gained as a result of hydraulic fracturing. As recommended, a practical way for improving the well productivity of the studied well, with respect to reservoir characteristic and existing operational condition, is use of fracturing methods. In general, the understudy well is a good example to being familiar with the most prevailing cause of well productivity loss in gas condensate reservoirs.

Minidrillstem Tests To Characterize Formation Deliverability in the Bakken

Summary Characterization of reservoir deliverability is fundamental for the economic development of any field. In the Bakken, there is a need for reliable pressure-transient tests to provide the effective formation permeability of the fracture/matrix system in this formation for deliverability calculations. This effective permeability can then be compared with laboratory-measured core permeability of the matrix rock samples. This comparison is the basis for planning early-production options and subsequent enhanced-oil-recovery (EOR) decisions. This comparison is particularly important because of the influence of massive hydraulic-fracture stimulation on reservoir performance. Determining well-deliverability potential by conventional drill-stem tests (DSTs) or traditional wireline formation tests (WFTs) in the past has resulted in mixed success in the Bakken. On the other hand, the mini-DST has increased the reliability of pressure-transient tests because the formation interval of interest is produced at a precise constant rate into a chamber between two inflated packers with negligible wellbore-storage effects. Also, the operation of a mini-DST tool requires much less time than the classical DST, and multiple zones can be tested sequentially to assess the individual-zone deliverability. The mini-DST tool uses the conventional WFT configured with a dual-packer module and downhole pump. Tests are conducted by inflating the dual-packer module to isolate a 3-ft interval of the wellbore. The formation fluid is pumped out from the packer-isolated wellbore interval to conduct pressure-drawdown and -buildup tests in the interval. An overlay of all the pressure-drawdown and -buildup results from various intervals is compared on a single plot to identify the most productive interval. Finally, conventional pressure-transient analyses are performed to interpret all pressure-drawdown and -buildup tests. In this paper, we present several field tests that were analyzed both by the preceding procedure and by numerical simulation. The analyses of several mini-DST results have provided insight into a better understanding of the flow mechanism in the Bakken both during primary production and in forecasting various improved-recovery and EOR proposals. The results can also serve as a basis for test design in similar low-permeability reservoirs elsewhere.

Uji ketahanan galur padi terhadap wereng coklat biotipe 3 melalui population build-up

Screening of rice lines resistance to brown planthopper (BPH) through mass screening, filtering line resistance and the population build-up are essential for the release of resistant rice varieties. In addition, the stages of the endurance are important in determining the stability of resistance, as well as the type of resistant. The research was carried out in the screen house at Indonesian Center for Rice Research in 2007. The BPH used in the research was the off spring of BPH biotype 3 that had been rearing on IR42 (bph2) variety since 1994. The result of this research showed that 22.2% of 18 lines/varieties were moderately resistant to BPH biotype 3ft namely BP4130-1f-13-3-2*B, BP4188-7f-1-2-2*B, BP2870-4e- Kn-22-2-1-5*B, and Pulut Lewok. On the population build-up test, the above lines/varieties were moderately resistant to BPH biotype 3pb. The low FPLI values were found in BP4130-1f-13-3-2*B and Pulut Lewok. The highest tolerance index was found on BP4130-1f- 13-3-2*B and Pulut Lewok followed by BP2870-4e-Kn-22-2-1-5*B and BP4188-7f-1-2-2*B. Pulut Lewok has the highest antibiosis index and is not significantly different to BP4130-1f-13-3-2*B, while BP4188-7f-1-2-2*B was lowest. Although Pulut Lewok has antibiosis defense mechanism, it is not tolerant to BPH biotype 3. The BP4130-1f-13-3-2*B line have both antibiosis and tolerant to BPH biotype 3. BP4188-7f-1-2-2*B line has tolerance character, but does not have character of antibiosis to BPH biotype 3.

Formation-Tester Pulse Testing in Tight Formations

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 155037, ’Formation-Tester Pulse Testing in Tight Formations (Shales and Heavy Oil): Where Wellbore-Storage Effects Favor the Determination of Reservoir Pressure,’ by Hamid Hadibeik, SPE, The University of Texas at Austin; Mark Proett, SPE, Dingding Chen, SPE, and Sami Eyuboglu, SPE, Halliburton; and Carlos Torres- Verdin and Rooholah A. Pour, The University of Texas at Austin, prepared for the 2012 SPE Americas Unconventional Resources Conference, Pittsburgh, Pennsylvania, 5-7 June. The paper has not been peer reviewed. Tight-formation testing, when mobilities are lower than 0.01 md/cp, poses significant challenges because conventional pressure-transient buildup testing becomes impractical because of the long buildup-stabilization time. An automated-pulse-test method is introduced for testing tight formations. It reduces testing time significantly and makes determination of formation pressure and permeability possible. Based on pressure data during the shut-in period, the next drawdown or injection test is designed such that the flow rate is a fraction of the initial pulse rate, followed by another shut-in test. This procedure continues until the difference in pressure at the beginning and at the end of the shut-in period is reduced to within a specified limit of pressure change; then, an extended transient is recorded to a stabilized shut-in pressure. Introduction Reservoir properties, such as formation pressure and permeability, can be measured with formation testers. Fluid sampling in laminated reservoirs under the influence of dynamic mud-filtrate invasion was tested by use of various probe-type formation testers. A complication in testing tight formations is that the measured pressure is supercharged and is greater than the reservoir pressure. The measured shut-in pressure usually is assumed to be the formation pressure. In a permeable formation, mudcake can form quickly and normally is very effective in slowing down invasion and maintaining the wellbore-sandface pressure near the formation pressure. However, this assumption is unrealistic, especially in low-mobility formations for which there could be no sealing mudcake to isolate the reservoir from hydrostatic pressure. In tight formations, the invasion rate is slowed by the formation, and mudcake may form slowly or not at all. As a result of the lack of sealing mud-cake, the pressure measured in these cases is substantially greater than the formation pressure. A pulse-test technique was used in combination with the spherical-flow model to obtain the true formation pressure. The early transient- and spherical-flow period can be distinguished from the late-transient-flow period by calculating the stream-line evolution of flow near the source. To measure the reservoir pressure in tight-formation testing, current technologies require several hours of wait time to reach the stabilized pressure, but often it is difficult to reach stabilization or to determine when it occurs. The automated-harmonic-testing method introduced here reduces the testing time substantially when a packer- or probe-type formation tester is used, and it automatically converges to the shut-in pressure.

A Variable-Rate Solution to the Nonlinear Diffusivity Gas Equation by Use of Green's-Function Method

SummaryThe hydraulic diffusivity equation that governs the flow of compressible fluids in porous media is nonlinear. Although the gas-well test analysis by means of the pseudopressure function has become a standard field practice, the effect of viscosity and gas-compressibility variation with pressure is often neglected. Moreover, in field operations, the gas well is submitted to a variable rate production to determine well/reservoir properties and an estimation of the absolute open flow (AOF). For slightly compressible fluids, variable rate can be properly handled by superposition in time. Unfortunately, superposition cannot be casually justified for gas reservoirs because of its nonlinear behavior.In this paper, a general solution that properly accounts for both fluid property behavior and variable rate is presented. The proposed solution, which is derived from the Green's-function method by recasting the effect of the viscosity-compressibility product variation as a nonlinear source term, can handle variable gas rate for several well/reservoir geometries of practical interest. From the general solution, an analytical expression for variable-rate tests of a fully penetrating vertical well in an infinite gas reservoir is derived. This expression is applied to a synthetic data set to calculate the pressure response for a buildup test in an infinite homogeneous reservoir. The results compared with a commercial finite-difference numerical simulator show close agreement for both drawdown and buildup periods. It is also shown that the dimensionless pseudopressure converges to the slightly compressible fluid solution for long shut-in times. Thus, during those long times, Horner analysis and log-log derivative plot can be applied to obtain good estimation of reservoir parameters, as discussed previously in literature.

Study on Test Cycle of Build-up Well Test in Low Permeability Reservoir

The speed of development of well test technology has been faster than well test interpretation technology in low permeability reservoirs. One of the main research directions for well test soft technology was specific interpretation theory and interpretation techniques. In recent years, well test was put forward higher request by the production complex and low permeability reservoirs. Test interpretation results urgently need to be applied to reservoir engineering analysis in-depth and quantitatively. One of the limited reality conditions of well test application was lack of the comprehensive research combined with the reservoir engineering. Combining with the test examples, the investigation radius change between injection-production wells was studied, and the build-up well test cycle in low permeability reservoir was optimized. According to the actual process situation, it was proposed that take 20d as the upper limit of well test cycle, and 10d block as the lower limit of well test cycle of build-up well test in a typical low permeability reservoir.

Discussion on the Disappearance of Transition Flow of Fractured Gas Reservoir with Pressure Transient Analysis

In recent years, more and more fractured gas reservoirs were discovered in the world. In general, fractured gas reservoirs are defined as formation with double porosity system, which is composed with fissure and matrix. In reservoirs with double porosity system, only the fissure system are connected with the wellbore and have relatively high permeability, matrix rocks have very low permeability, gas can flow into the wellbore only via fissures, and the flow process be divided into the flow in fissures, transition flow and the flow in the total system. But transition flow is not found in the process of well testing, which results in misapplication of development decision support and selection in gas field development program. In this paper, the influent factors of fractured gas reservoir for estimation are studied by models of single well simulation, and the simulated results are analysis by the method of pressure transient analysis. For example: the time of pressure build-up test, production time, wellbore storage coefficient,kv/kh,the reservoir boundary, the pressure precision, the porosity of matrix and fracture, the permeability of matrix and fracture, the thickness of formation(partial perforation),skin, water saturation etc. The results of simulation show that the disappearance of the transition flow is caused by many factors, which include that the time of pressure build-up test is short, production time is not sufficiently long, ,the vertical permeability is much larger than the horizontal permeability and the formation is perforated partially, the time of the reservoir boundary for pressure is short than the transition flow, the porosity of matrix is close to the porosity of fracture, the permeability of matrix much smaller than the fracture permeability, the pressure precision is low. The transition flow is not affected by the skin, the wellbore storage coefficient and water saturation, which cover up the radial flow in fissure system.

Modeling the hyperviscoelastic behavior of a tire tread compound reinforced by silica and carbon black

AbstractThis research study was devoted to the modeling of the mechanical behavior of three carbon black/silica natural rubber/butadiene rubber (NR/BR) compounds under a tensile load. These compounds were prepared on a two‐roll mill, and the tensile testes were carried out on a dumbbell‐shaped specimen and three rubber‐strip specimens with different widths. Heat buildup tests were also performed, and the temperature rise was determined. The time‐independent behavior of the rubber was described by traditional hyperelastic models, including those of Marlow and Yeoh. The viscoelastic behavior was studied with two linear (Prony series) and nonlinear [Bergstrom–Boyce (BB)] models. A previously developed methodology by the authors, which was based on the finite element modeling of the tension of the rubber strips, was used to determine the parameters of the mentioned equations. It was shown that neglecting the viscoelasticity would have given rise to large errors in predicting the mechanical deformation in the rubbers. However, the linear viscoelastic model failed to predict the correct behavior at a large strain, particularly for wider samples. On the other hand, not only could the combination of the Yeoh hyperelastic model with the BB equation describe the mechanical behavior at low to medium strains, but also the large strains were taken into consideration. Both the linear and nonlinear hyperviscoelastic models accurately described the hysteresis in rubbers, and this could be used for the evaluation of the rolling resistance in tires. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Successful Applications of Pressure-Rate Deconvolution in the Cad-Nik Tight Gas Formations of the British Columbia Foothills

Summary The Cadomin-Nikanassin (Cad-Nik) sandstone formations in the Lower Cretaceous reservoirs along the reverse-thrust faulting belt of northeastern British Columbia (NEBC), Canada, have emerged in recent years as a new tight gas play. The low porosity (3?6%) of the rock matrix controls gas storativity, while the presence of natural fractures in the form of clusters or swarms allows significant and sustainable flow rates for commercial production. Newly drilled wells are commonly hydraulically fractured to establish or enhance wellbore connectivity to the natural-fracture network. Seismic mappings of these structural unconventional-gas reservoirs provide the early assessments of resource sizes and initial gas in place (IGIP), which usually bear large uncertainties because of the difficulty in determining reservoir structural closures and pay-porosity cutoffs. Regional analogue wells are often used to guide development decisions. Meanwhile, estimating connected reservoir volumes through conventional-gas material balances (p/z vs. cumulative production) and production-data analysis [rate-transient analysis (RTA)] has not been without challenges. Fairly long pressure buildups (PBUs), on the order of hundreds of hours, are often performed without seeing the pressure stabilization required to estimate accurately the reservoir pressure needed for material-balance calculations. The applicability of pressure extrapolation to these tests has not been systematically investigated; therefore, no reliable methods for using shorter shut-ins to estimate reservoir pressure currently exist. Thus, reliable average reservoir-pressure estimates require significantly longer well shut-in times in order to perform meaningful gas material balance. Because this is not practical, confidence in material-balance results requires a second, independent method for establishing connected well volumes to be used in comparisons and cross checking. One possible choice is RTA, but, in these fields, numerous times wellhead-pressure data are also unavailable or unreliable. This paper presents two field-case studies that demonstrate the successful application of the pressure/rate-deconvolution approach, combining a well?s long, high-quality production-rate history with accurate downhole-pressure data from relatively short buildup tests. This approach allows the reservoir engineer to (1) reconcile the performance-based estimated-ultimate-recovery estimates with the volumetric IGIPs; (2) establish, at the least, minimum well-drainage size and connected volume; and (3) select possible infill-drilling opportunities. A final benefit is that this often leads to a better understanding of well/reservoir parameters.

Production performance of hydraulic fractures in tight gas sands, a numerical simulation approach

Hydraulically fractured tight gas reservoirs are one of the most common unconventional gas sources being produced today, and will be a regular source of gas in the future. The extremely low permeability of tight gas sands leads to inaccuracy of conventional build-up and draw-down well test results. This is primarily due to the increased time required for transient flow in tight gas sands to reach pseudo-steady state condition. To increase accuracy, well tests for tight gas reservoirs must be run for longer periods of time which is in most cases not economically viable. The large amount of downtime required to conduct well tests in tight sands makes them far less economical than conventional reservoirs, which leads to the need for accurate simulation of tight gas reservoir well tests.This paper presents simulation results of a 3-D hydraulically fractured tight gas model created using Eclipse software. The key aims are to analyze the effect of differing fracture orientation, number and length. The focus of the simulation runs will be on the effect of hydraulic fracture orientation and length. The results will be compared to simulation runs without the abovementioned factors to determine their effects on production rates and well performance analysis. All results are plotted alongside an un-fractured tight gas scenario in order to put the hydraulic fracture performance in perspective.Key findings from this work include an approximately linear relationship between initial gas rate and the number of hydraulic fractures intersecting the wellbore. In addition, fracture length is found to have less of an impact on initial gas rate compared to number of fractures intersecting the wellbore, for comparable total fracture volumes.

Transient Nonisothermal Fully Coupled Wellbore/Reservoir Model for Gas-Well Testing, Part 2: Applications

Summary After the development of a numerical fully implicit nonisothermal wellbore/reservoir simulator in Part 1 of this study (Bahonar et al. 2010), this simulator is implemented for a close and detailed study of gas-well pressure-drawdown (DD) and -buildup (BU) tests. Overall, the developed simulator is an accurate and strong tool for design and analysis of transient gas-well testing, particularly for high- pressure/high-temperature (HP/HT) gas reservoirs. Several numerical results will be presented. This includes demonstration of the behaviour of the wellbore-fluid pressure, temperature, density, and velocity and an overall heat-transfer coefficient during DD or shut-in tests for nonisothermal reservoirs and conceptual comparisons with the isothermal counterparts. Thermal effects on the behaviour of derivative plots and the sandface-flow rate of deep nonisothermal gas reservoirs will be studied. A significant effect of neglecting the heat capacity of tubular and cement materials on the wellhead-temperature simulation, and thus transient well tests, will be demonstrated. A sample case to show that neglecting the thermal effects in the gas-well tests of composite reservoirs leads to unreliable results in well-testing analysis will be presented. Several other numerical experiments, including the presence of a variable wellbore-storage coefficient, gas backflow from the wellbore to the reservoir, and other thermal effects during the gas-well tests, are also presented. Hundreds of millions of dollars are spent every year on well testing around the world (Hawkes et al. 2001). A proper design and truthful interpretation of these tests can be achieved by a reliable coupled wellbore/reservoir simulator, which in turn can save a large portion of the required costs.

Characterization of well skin using buildup test and radon as a tracer

Pressure buildup tests are often used to determine the reservoir permeability and skin factor to quantify formation damage. However, no quantitative method is currently available for calculating the reduced permeability of the skin zone. With the help of radon measurements during the flow period preceding the buildup test, it is possible to calculate both the radius and the altered permeability in the damaged zone based on a radial composite model.

Prediction of heat build-up of solar reflecting coatings based on physico-chemical properties of complex inorganic colour pigments (CICPs)

Heat build-up of coated surfaces – such as roofs, facades and other construction elements, as well as fuel tanks, cooler jackets and warehouses – due to solar radiation and the resulting temperature increase of interiors is highly undesirable and can even be dangerous. One of the methods used to decrease the heat build-up of surfaces is the subsequent application of pigmented organic coatings with high IR reflectance properties. Investigations of the morphology, chemical composition and optical properties of complex inorganic colour pigments (CICPs) were performed and the heat build-up of the coatings was measured. The sedimentation method and laser scattering method were used to determine particle sizes and particle size distribution. The composition of pigments and shape of their particles were evaluated by energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). Phase analysis was carried out by the X-ray diffraction method (XRD). Spectral characteristics of pigments were measured at wavelengths from 250 nm to 2500 nm. The total solar reflectance (TSR) was calculated according to ASTM E903. Heat build-up testing was carried out in a box designed and constructed according to ASTM D4803. Mathematical methods were used to describe dependencies between the tested variables. These dependencies may serve as data that allow to predict heat build-up of coated surfaces as a consequence of the absorption of solar energy.

Investigation of Effect of Fracturing Fluid on After-Closure Analysis in Gas Reservoirs

Summary Published techniques for analysis of after-closure fracture data usually assume single-phase flow. These procedures generally rely on the techniques developed for the analysis of buildup tests. Applying the buildup techniques implies that the injected fluid and reservoir fluid have approximately the same properties. This assumption is generally incorrect in case of minifrac tests where the injected fluid may be very different from the reservoir fluids. This situation is at an extreme when the minifrac test is conducted on a gas reservoir and the injected fluid may be a relatively high-viscosity gelled fluid. In this paper, we review the basic theory behind after-closure analysis. Using a numerical simulator, minifrac tests are simulated and analyzed for both oil- and gas-reservoir cases where an aqueous phase is injected as a fracturing fluid. Analyses of the numerically simulated falloff data are presented. Guidelines for the analysis of such data have been developed and presented. Field data are also presented. In one case, breakdown, step-rate, and fluid-efficiency tests (FETs) were performed on a tight gas formation and the data were analyzed. The results of using these various techniques are presented. The consistency of results validates conclusions achieved using the numerically simulated data.

Fast evaluation of the fatigue lifetime of rubber-like materials based on a heat build-up protocol and micro-tomography measurements

The temperature of rubber-like materials increases under cyclic loadings, due to their dissipative behaviour and low thermal conductivity. This well-known phenomenon, called heat build-up, has attracted the attention of researchers for a long time. But, to our knowledge, no published studies have tried to link this temperature rise to fatigue behaviour, as already done for many metallic materials. Two main points are discussed in this paper. The first one is dedicated to heat build-up measurements: a specific experimental protocol was developed to capture the instantaneous heat build-up and, based on this protocol, a “heat build-up test” was defined in order to link the temperature rise to the principal maximum strain, which is a commonly used variable for fatigue criterion. A discussion on the correlation between these results and the fatigue behaviour is opened. This relation is illustrated for several industrial materials by a comparison between heat build-up measurements and fatigue life duration. The second point investigates the ability to couple X-ray tomography measurements presented elsewhere [1] to the former heat build-up results in order to predict the initiation lifetime. An approach based on a critical energy criterion was proposed and the comparison to a classic Wöhler curve approach gave very good results.

Build-up and long-term performance test of a full-scale solar-assisted heat pump system for residential heating in Nordic climatic conditions

This paper presents the build-up and long-term performance test of a full-scale Solar-Assisted Heat Pump System (SAHPS) for residential heating in Nordic climatic conditions. This particular SAHPS was developed within the EU project ENDOHOUSING, by predominantly using components and techniques that are available on the market. The analysis primarily focuses on system performance, with emphasis on Heat Pump (HP) and total system Seasonal Performance Factor (SPF), based on long-term and full-scale operation. Analysis shows that despite unfavourable building conditions, for low energy use and utilisation of a SAHPS, the system was successfully in full operation (for about 2 years) fulfilling heating requirements. Data processing of the series representing the full year period of 2007(February)–2008(February), presented a HP and total SAHPS performance of: SPF HP = 2.85 and SPF SAHPS = 2.09. The authors argue that with an optimised SAHPS control and operation strategy, additional use of circulation pumps and energy (electricity) could be vastly reduced, hence attaining a SPF SAHPS value that is in parity with the SPF HP . As the Nordic (Swedish) Endohousing SAHPS has not yet been properly optimised/designed and installed in an appropriate house, the SPF HP = 2.85 is considered satisfactory.

Estimate of In-situ Permeability and Fluid Flow Paths from Hypocenter Migration of Microearthquakes during the Build-up Tests of Geothermal Wells in the Takinoue Geothermal Area

Estimate of In-situ Permeability and Fluid Flow Paths from Hypocenter Migration of Microearthquakes during the Build-up Tests of Geothermal Wells in the Takinoue Geothermal Area

When does a longer shut-in lead to a larger radius of investigation?

While the concept of radius of investigation is better understood for drawdown tests, its applicability to buildup tests is less certain. For example, a rule of thumb is that “one cannot see a particular feature in a buildup unless the radius of investigation during the preceding flow period has seen that feature”. In this paper, we clearly illustrate that the radius of investigation of a buildup can be larger than that of its previous flow period. Another common contention is that the radius of investigation of a buildup is limited by noise dominating the late-time pressure behavior. Oliver [Oliver, D.S., 1990. The averaging process in permeability estimation from well-test data. SPEFE. pp. 319–324.] and later Thompson and Reynolds [Thompson, L.G. and Reynolds, A.C, 1997. Well testing for radially heterogeneous reservoirs under single and multiphase flow conditions. SPEFE. pp. 57–64.] defined the radius of investigation based on the distance from the well to the region of the reservoir which has the greatest impact on the pressure derivative. We have used this approach to calculate the derivative and show that the ratio of noise to the signal from the reservoir does not necessarily increase. While many situations exist when radius of investigation of a build-up test is limited by the preceding flow period and noise, we show that when data is sampled appropriately, the radius of investigation of a buildup can easily go beyond that of the preceding flow period, and demonstrate when this may remain unaffected by noise.

Technology Focus: Well Stimulation (June 2009)

Technology Focus It is important to put the role of well stimulation into perspective as key to driv-ing production and competing in the world's energy market. Interesting information can be found in the US DOE Energy Information Agency's report Table 11.1 World Primary Energy Production by Source, 1970–2005, which is available at http://www.eia.doe.gov/aer/txt/ptb1101.html (accessed 7 April 2009). Oil last peaked as the world's primary energy source in 1973 at just more than 47% of all sources. By 2005, this number had dropped to approximately 34%, although the world's total energy production had nearly doubled over these 32 years. While coal remained fairly steady at 25 to 27% of the world's market share, natural-gas and natural-gas-liquid (NGL) usage increased from 20 to 25%. This suggests that natural gas could surpass oil and coal as the world's primary energy source within the next decade or so, unless low natural-gas prices continue. Renewable-energy sources (e.g., nuclear, hydroelectric, and geothermal) gained an increase in total market share from 7 to nearly 14%, with these sources supplying more than 63 quadrillion Btu to the world in 2005 alone. Natural gas and NGLs had not surpassed this level until 1984, just 21 years earlier. Renewable energy has doubled its market share during a doubling of the market size. To improve recovery, well-stimulation tests, data, and interpreters need to become valuable commodities on par with the other well costs. Data and analysis provide a basis for improvement. Whether success may come from higher retained conductivity, comparing pre- vs. post-treatment buildup tests, or acquiring bottomhole treating pressures to unmask friction effects, many avenues are available to enable us to compete at the next level. We need to embrace our best practices, strive for new developments, and analyze much more data to perform at the next level. Without measuring results, we cannot prove the improvements. Although oil may be nearing its end as the world's primary energy source, it is doing great as a source of products. To transition to natural gas as the new energy leader, well stimulations will be a key to keeping the petroleum industry as the world's best provider of clean and cost-effective energy. Please enjoy reading the following selections representing the future of well stimulations and interesting examples of how we can compete. Well Stimulation additional reading available at the SPE eLibrary: www.spe.org SPE 119623 • "Acid Fracturing: The Effect of Formation Strength on Fracture Conductivity" by A.M. Gomaa, SPE, Texas A&M University, et al. SPE 121483 • "First North Sea Application of Pinpoint-Stimulation Technology To Perform a Rig-Based Acid-Fracture Treatment Through CT" by David Barclay, SPE, Halliburton, et al. SPE 116775 • "An Innovative Acid-Stimulation Technique for Reviving Dead Wells in the Ghawar Field of Saudi Arabia—A Holistic Approach" by Surajit Haldar, SPE, Saudi Aramco, et al.