Blasingame Type Curves Research Articles

Analysis of Production Decline Type Curves Considering Water Influx in Naturally Fractured Gas Reservoirs

Abstract In the development of fractured gas reservoirs with edge and bottom water, water invasion is a pervasive issue. However, most production decline analysis models focus on primary depletion with closed boundaries rather than secondary depletion with water influx. Therefore, this paper aims to develop decline type curves for analyzing and interpreting production data from existing natural water influx in fractured gas reservoirs. Firstly, a transient dual porosity flow model is developed considering water influx in naturally fractured gas reservoirs, the functions of Blasingame decline type curves are derived and obtained. Subsequently, the Blasingame production decline type curves of a vertical well in naturally fractured reservoirs experiencing natural water influx are plotted. These new type curves can estimate water invasion and dual medium parameters, offering valuable insights for production decline analysis in fractured reservoirs with water influx. The Blasingame production decline curves are divided into six regimes based on characteristics. Then, the effects of various formation parameters and water invasion cases on the type curves are discussed and analyzed. Compared with Blasingame type curves without water influx at the external boundary, the behaviors of those presented in this paper are quite different at the boundary responses. Finally, through the analysis of a case well, it is found that theoretical type curves considering dual-medium and water invasion are more consistent with actual production data. This suggests that these new type curves provide more accurate estimation for understanding and managing issues related to water invasion in fractured gas reservoirs.

Production Decline Analysis of Tight Conglomerate Reservoirs with Small Well Spacing, Based on the Fractal Characteristics of Fracture Networks

The conglomerate matrix and fracture propagation are special in tight conglomerate reservoir with small well spacing. In this article, the fractal propagation characteristics of the fracture network in conglomerate reservoirs are described by experiment and a micro-mathematical model. According to the core slice, the conglomerate reservoir matrix presents the multi-modal pore structure, described as the “pseudo-dual-media” model. Given the above, the unsteady seepage mathematical model, comprehensively considering the fractal fracture network, stress sensitivity of main fractures, and threshold pressure gradient of the reservoir matrix, was developed and analytically solved. The Blasingame type curves for production decline analysis were plotted, and the sensitive parameters were analyzed. The field application was performed for validation. The research results show that the fractal dimension decides the complexity of the fracture network distribution. As it increases, the unsteady flow occurs earlier, and the boundary flow is delayed. The anomalous diffusion exponent represents the smoothness of crude oil migration and a higher value leads to higher resistance to oil migration and larger pressure drawdown for the same production rate. The growth of the threshold pressure gradient within a certain range can result in a localized downward shift of the type curves. The field application in a conglomerate oil reservoir showed that the presented model presents a fitting accuracy 10% higher than that of the conventional SRV model and has high reliability and precision for the production performance evaluation of the small-well-spacing development of tight conglomerate reservoirs.

Well Interference Analysis of Shale Gas Wells Based on Embedded Discrete Fracture Model

Well interference is commonly observed in shale gas reservoirs due to the small well spacing, and it significantly affects the shale gas production. Effective evaluation of well interference is important to increase the gas production of shale gas wells. Previous researches mainly focus on the well interference phenomenon and production optimization using numerical simulation so that the quantitative analysis of shale gas well interference is rare. Therefore, this paper is aimed at analyzing the well interference of shale gas wells through production type curves. First, the complex fracture networks are described by using the embedded discrete fracture model (EDFM). Second, different cases are designed to characterize different types and degrees of well interference in shale gas reservoirs. Third, numerical modelling is conducted to simulate the well interference and its effect on gas production. Fourth, the type curves are obtained to quantitatively analyze and compare the impact of well interference on shale gas production. Results show that well interference caused by hydraulic fractures mainly reduce the gas production of the parent well while the gas production of child well can be increased owing to the larger equivalent stimulated area. The pressure depletion is obvious when the well communication degree becomes higher. Differences can be found from early to late periods by the combination of log-log and Blasingame type curves. This work provides a method for well interference evaluation, and it can be used to obtain well spacing and adjust fracturing parameter in shale gas reservoirs.

Incremental and acceleration production estimation and their effect on optimization of well infill locations in tight gas reservoirs

The main role of infill drilling is either adding incremental reserves to the already existing one by intersecting newly undrained (virgin) regions or accelerating the production from currently depleted areas. Accelerating reserves from increasing drainage in tight formations can be beneficial considering the time value of money and the cost of additional wells. However, the maximum benefit can be realized when infill wells produce mostly incremental recoveries (recoveries from virgin formations). Therefore, the prediction of incremental and accelerated recovery is crucial in field development planning as it helps in the optimization of infill wells with the assurance of long-term economic sustainability of the project. Several approaches are presented in literatures to determine incremental and acceleration recovery and areas for infill drilling. However, the majority of these methods require huge and expensive data; and very time-consuming simulation studies. In this study, two qualitative techniques are proposed for the estimation of incremental and accelerated recovery based upon readily available production data. In the first technique, acceleration and incremental recovery, and thus infill drilling, are predicted from the trend of the cumulative production (Gp) versus square root time function. This approach is more applicable for tight formations considering the long period of transient linear flow. The second technique is based on multi-well Blasingame type curves analysis. This technique appears to best be applied when the production of parent wells reaches the boundary dominated flow (BDF) region before the production start of the successive infill wells. These techniques are important in field development planning as the flow regimes in tight formations change gradually from transient flow (early times) to BDF (late times) as the production continues. Despite different approaches/methods, the field case studies demonstrate that the accurate framework for strategic well planning including prediction of optimum well location is very critical, especially for the realization of the commercial benefit (i.e., increasing and accelerating of reserve or assets) from infilled drilling campaign. Also, the proposed framework and findings of this study provide new insight into infilled drilling campaigns including the importance of better evaluation of infill drilling performance in tight formations, which eventually assist on informed decisions process regarding future development plans.

A Practical Methodology for Production Data Analysis in Carbonate Reservoirs Using New Decline Type Curves

Carbonate reservoirs typically have complex pore structures, so the production wells typically have high production in the early production stage, but they decline rapidly. It is highly challenging to achieve accurate interpretation results. In this paper, a new and practical methodology for production data analysis of fractured and fractured-vuggy carbonate reservoirs is proposed. Firstly, analytical solutions to characterize the different multipore media and simulate transient production behavior of fractured and fractured-vuggy carbonate reservoirs during the transient flow regime are presented. Then, a new function f q D and f ′ q D that related to the dimensionless production rate is introduced, and a series of new decline type curves are drawn to make a clear observation of different flow regimes. In addition, the effects of the storativity ratio, interporosity flow coefficient, skin factor, and dimensionless radial distance of external boundary on production performance are also analyzed. Finally, two example wells from the fractured and fractured-vuggy carbonate reservoirs are used to perform rate decline analysis with both the Blasingame type curves and the new type curves. The validation of the new method is demonstrated in comparison to the results of well test interpretation. The results show that the curves of 1 / f ′ q D vs. t D are ∧ -shaped for dual-porosity reservoirs and M -shaped for triple porosity reservoirs and also indicate that the interpreted parameters such as permeability, skin factor, storativity ratio, and interporosity flow coefficient using new decline type curves are aligned well test interpretation. In correlation with other traditional well test analysis, this approach effectively reduces the multisolution probability of interpretation.

Semi-analytical modeling of transient rate behaviour of a horizontal well with multistage fractures in tight formations considering stress-sensitive effect

Stress-sensitive permeability imposes a significant impact on production performance in a tight formation; however, the widely used models assume the constant permeability or same stress-sensitive level for different systems, resulting in incorrect prediction of production rate and reservoir properties. In this work, theoretical models have been formulated, validated, and used to characterize the transient rate behaviour of a horizontal well with multistage fractures at constant wellbore pressure in tight formations by taking the different stress-sensitive effects in matrix and fracture subsystems into account. More specifically, a matrix-fracture fluid flow model with considering stress-sensitive effect was developed, during which the resulting nonlinear governing equation caused by stress-sensitive matrix permeability was weakened and linearized by using the Pedrosa's transform formulation and perturbation technique, respectively. Then, a slab source function was developed to obtain the solution for such a linearized problem in the Laplace domain. Meanwhile, a semi-analytical method is applied to solve the matrix-fracture flow models by discretizing each hydraulic fracture into small segments. Furthermore, the Blasingame type curves are generated to examine the stress-sensitive effects. In particular, stress-sensitivity in matrix and hydraulic fracture subsystems can be respectively analyzed. It is found that stress-sensitive permeability in either the matrix subsystem or the fracture subsystem has its negative influence on production rate. Such an influence is increased as the permeability modulus in matrix and fractures is increased. The matrix permeability modulus mainly decreases the production rate in the intermediate and late flow period, while its effect on the early time production rate is relatively small compared with other flow periods. Stress-sensitivity in fractures mainly affects the early time production rate and imposes a negligible impact on production rate during the intermediate and late period. The production rate is increased with an increase in the initial fracture conductivity. The dominant flow which contributes to the majority of the total production gradually shifts from the near-wellbore fracture segments to the near-tip fracture segments for the intermediate and high conductive fracture cases, while, for the low conductive fractures, the near-wellbore fluid flow is dominant for the entire period. Due to the inherent constraints in a tight formation, rate transient analysis is found to be more physically representative for accurately describing performance of a horizontal well with multistage fractures compared to the traditional pressure transient testing.

Production Decline Behavior Analysis of a Vertical Well with a Natural Water Influx/Waterflood

The production decline type curves are considered as a robust technique to interpret the production data and obtain the flow parameters, the original gas in place, etc. However, most of the previous models have focused on the primary depletion with a closed boundary, rather than on the secondary depletion with a water influx/waterflood. Therefore, in this study, a transient flow model considering the water influx/waterflood is developed. Subsequently, the functions of the production decline type curves for a vertical well with a water influx/waterflood are derived based on the material balance equation. In other words, the theory of Blasingame production decline analysis is extended to the water influx/waterflood reservoir. Further advanced Blasingame production decline type curves for a vertical well in water influx/waterflood reservoirs are generated. Compared with Blasingame type curves without a water influx/waterflood, the behavior of the ones presented in this study is quite different at the boundary. Thereafter, the effects of the relevant parameters, including the dimensionless maximum water influx, the dimensionless beginning time of the water influx, and the dimensionless external boundary radius, are studied on type curves. Finally, Blasingame type curves for a vertical well in water influx/waterflood reservoirs are verified through a field case study. This work provides very meaningful references for reservoir engineers working on the evaluation of the water influx and the estimation of the beginning time of the water influx by matching the developed type curves with the actual field data.

Blasingame decline analysis for variable rate/variable pressure drop: A multiple fractured horizontal well case in shale gas reservoirs

Advanced production decline analysis methods have become more economic and efficient options due to technical and time limitations of well-testing operations in shale gas reservoirs. By normalizing rate with material balance pseudo-time, Blasingame type decline analysis can be applied to variable rate/variable pressure drop system, making the methodology more widely applicable. Blasingame decline analysis of variable rate/variable pressure drop case for multi-fractured horizontal well (MFHW) in shale has been less investigated, because of multi-scale storage spaces and multi-flow mechanisms. This article presents a semi-analytical Blasingame decline analysis model incorporating multi-flow mechanisms with shale's modified material balance pseudo-time. Laplace transformation, point source function, numerical discrete method, perturbation method, and Gaussian elimination method were employed to solve the mathematical problem caused by multi-flow mechanisms. Besides, the material balance pseudo-time was modified by considering adsorption and desorption. In this study, a workflow to investigate the effects of properties of hydraulic fracture (fracture half-length, number of fractures and fracture spacing) and multi-flow mechanisms (diffusion and desorption) on production decline behaviors through diagnostic Blasingame type curves is proposed. The results indicate that productivity is greater with a larger scale of fracture treatment, and better desorption of adsorbed gas is also beneficial to production. The decline rates affected by the fracture treatment scale and supplement capacity show two opposite trends, which is caused by interference between the fractures and boundary, respectively. Except that the data in the diffusion early flow period do not match very well, because the use of diffusion coefficient as a constant, the good fitting results on the whole verifies the model's validity and reliability.

Production data analysis in gas condensate reservoirs using type curves and the equivalent single phase approach

Most modern production data type curve (PDTC) techniques, which are used in the estimation of reservoir and well productivity parameters such as permeability, drainage radius and skin, were originally developed with the assumption of Darcy flow (i.e. laminar flow, with pressure gradient proportional to the fluid superficial velocity, in accordance with Darcy's law) of a single-phase fluid. Two-phase conditions, e.g. in a gas condensate reservoir (GCR) operating below dewpoint pressure, introduce nonlinearities into the diffusivity equation, making the use of single-phase techniques questionable, and potentially producing erroneous parameter estimates. A common approach to linearizing the system is by the use of pseudovariables which account for the two-phase effects in addition to the pressure-dependence of fluid properties.In this study, GCR production data generated using homogeneous fine-grid compositional simulation models, were first analysed using a well-known conventional (single-phase) modern PDTC technique, namely the Blasingame type curves for radial flow around a vertical well in a circular drainage area. The conventional techniques were then modified using an equivalent single phase concept, which was employed in the computation of two-phase pseudovariables for use with the single-phase PDTC. To compute these two-phase pseudovariables, pressure-saturation/kr relationships are required. These were determined using a technique, which employs fluid component weight fractions and gas fractional flow of a fluid with constant fixed total composition. Sensitivities were conducted on reservoir fluid richness (maximum liquid dropout from 1% to 42%), relative permeability curves, degree of reservoir undersaturation and well operating pressures, to examine their impact on production decline response and subsequent conventional PDTC analysis, as well as their impact on the effectiveness of the equivalent single-phase based approach used in this study.The paper first highlights the impact of two-phase flow conditions in GCRs on conventional PDTC analysis, in terms of the quality of the type curve match (TCM) and estimates of permeability, drainage radius and skin. Then it is shown that, in GCR analysis where the impact of two-phase effects are important, significant improvements can be obtained, both in the quality of the TCM and subsequent parameter estimates, through the use of pseudovariables computed using equivalent single phase concepts. The results also identify conditions under which, depending on the fluid richness and/or the degree of undersaturation, two-phase effects, although present, may not significantly impact the quality of interpretation of long-term production data from GCRs, using conventional single-phase PDTC techniques.

Rate Decline Analysis for Modeling Volume Fractured Well Production in Naturally Fractured Reservoirs

Based on the property discontinuity in the radial direction, this paper develops a new composite model to simulate the productivity of volume fractured wells in naturally fractured reservoirs. The analytical solution of this model is derived in detail and its accuracy is verified by the same model’s numerical solution. Detailed analyses of the traditional transient and cumulative rate are provided for the composite model. Results show that volume fracturing mainly contributes to the early-flow period’s production rate. As interregional diffusivity ratio increases or interregional conductivity ratio decreases, the transient rate at the same wellbore pressure increases. Three characteristic decline stages may be observed on transient rate curves and the shape of traditional rate curves in the middle- and late-flow periods depends on naturally fractured medium and boundary condition. By introducing a new pseudo-steady constant, new Blasingame type curves are also established and their features are more salient than those of traditional rate curves. Five typical flow regimes can be observed on these new type curves. Sensitivity analysis indicates that new Blasingame type curves for varied interregional diffusivity ratio, interregional conductivity ratio, interporosity coefficient and dimensionless reservoir radius, except storativity ratio, will normalize in the late-flow period.

Rate decline curves analysis of multiple-fractured horizontal wells in heterogeneous reservoirs

In heterogeneous reservoir with multiple-fractured horizontal wells (MFHWs), due to the high density network of artificial hydraulic fractures, the fluid flow around fracture tips behaves like non-linear flow. Moreover, the production behaviors of different artificial hydraulic fractures are also different. A rigorous semi-analytical model for MFHWs in heterogeneous reservoirs is presented by combining source function with boundary element method. The model are first validated by both analytical model and simulation model. Then new Blasingame type curves are established. Finally, the effects of critical parameters on the rate decline characteristics of MFHWs are discussed. The results show that heterogeneity has significant influence on the rate decline characteristics of MFHWs; the parameters related to the MFHWs, such as fracture conductivity and length also can affect the rate characteristics of MFHWs. One novelty of this model is to consider the elliptical flow around artificial hydraulic fracture tips. Therefore, our model can be used to predict rate performance more accurately for MFHWs in heterogeneous reservoir. The other novelty is the ability to model the different production behavior at different fracture stages. Compared to numerical and analytic methods, this model can not only reduce extensive computing processing but also show high accuracy.

Blasingame decline type curves with material balance pseudo-time modified for multi-fractured horizontal wells in shale gas reservoirs

Production decline analysis has been considered as a robust method to obtain the flow parameters, reservoir properties and original gas in place. Although advanced Blasingame production decline analysis methods for vertical wells, fractured wells and horizontal wells in conventional reservoirs are widely used, there is no Blasingame production decline type curves for multi-fractured horizontal wells (MFHW) with considering stimulated reservoir volume (SRV) in shale gas reservoirs yet. Compared with conventional gas reservoirs, multi-flow mechanisms (such as Darcy flow, diffusion and adsorption/desorption) and complex flow behaviors of MFHW exist in shale gas reservoirs, bringing a big challenge for analyzing the rate decline performance of the wells. Thus, in this paper based on the material balance equation in consideration of adsorption/desorption, the material balance pseudo-time of Blasingame decline type curves is modified so as to extend the theory of Blasingame production decline analysis to shale gas reservoirs. Considering the nonlinearity caused by gas desorption and diffusion, and the complex flow of MFHW, a numerical method is applied in this paper to obtain Blasingame type curves. Based on the perpendicular bisection (PEBI) grids, a numerical model considered SRV is developed and the solution is obtained using control volume finite element method and the fully implicit method. Further Blasingame type curve is validated by a simplify model, and Blasingame production decline type curves of the MFHW considering SRV in a shale gas reservoir are plotted through computer programming. Five flow regimes, including early formation linear flow, early radial flow, compound linear flow, the second radial flow and pseudo-steady flow, are recognized. Compared with the modified Blasingame type curves presented in this paper, the ones with traditional pseudo-time have a tendency to underestimate the value of normalized rate, normalized cumulative production, normalized integral derivative cumulative production and the reserve. The effects of relevant parameters including SRV radius, outer region radius, permeability in SRV region and outer region, Langmuir pressure, Langmuir volume and diffusion coefficient on type curves are analyzed as well. This work expands our understanding of a MFHW flow behaviors in shale gas reservoirs, which can be used to estimate with reservoir properties, SRV, and reserves in these types of reservoirs.

Analysis and Comparison of Decline Models: A Field Case Study of a Naturally Fractured Gas Condensate Reservoir

Decline curve analysis is one of the most commonly used techniques to predict future production performance and estimate reserves from routinely available production data. This article presents obtained results from production data analysis of a naturally fractured lean gas condensate reservoir with homogenous reservoirs decline curve analysis methods. Different methods were used to estimate reservoir original gas in place and expected ultimate recovery. Results have shown that traditional Arp’s equations and Fetkovich type curve cannot estimate original gas in place and expected ultimate recovery reliably; but the values of the Blasingame type curve and Agarwal-Gardner type curve can estimate them with about 8% error.

Rate decline analysis of multiple fractured horizontal well in shale reservoir with triple continuum

Multiple fractured horizontal well (MFHW) is widely applied in the development of shale gas. To investigate the gas flow characteristics in shale, based on a new dual mechanism triple continuum model, an analytical solution for MFHW surrounded by stimulated reservoir volume (SRV) was presented. Pressure and pressure derivative curves were used to identify the characteristics of flow regimes in shale. Blasingame type curves were established to evaluate the effects of sensitive parameters on rate decline curves, which indicates that the whole flow regimes could be divided into transient flow, feeding flow, and pseudo steady state flow. In feeding flow regime, the production of gas well is gradually fed by adsorbed gases in sub matrix, and free gases in matrix. The proportion of different gas sources to well production is determined by such parameters as storability ratios of triple continuum, transmissibility coefficients controlled by dual flow mechanism and fracture conductivity.

Applying Rate Transient Analysis (RTA) to integrate geological and engineering data

The Blasingame typecurve in Fekete’s Rate Transient Analysis (RTA) software has been used at Santos to increase the understanding and integration of well and reservoir data; however, the authors have discovered that in some cases the tool produced anomalous results, such as permeability being too low. The potential consequence of this was incorrectly writing off reserves or making projects (in particular compression projects) fail economic tests. After testing various hypotheses, a simple yet unorthodox solution was only discovered in a field where the anomaly was more profound, and required integrating geology and geophysics to explain it. This solution has since been applied in RTA models across numerous other fields, and it has improved the quality and confidence of these models. The solution was the realisation that in many cases the accessed gas in place (GIP) increased over time, but the underlying model in RTA assumes a single tank, linear P/z. Matching the RTA model with the initial reservoir pressure and final accessed GIP results in over-predicting the reservoir pressures, resulting in an artificially low permeability. The authors discovered that the appropriate well and reservoir parameters could be obtained by matching the late time data using a lower initial reservoir pressure value corresponding to when the well had accessed the final GIP volume but not the initial reservoir pressure. This step was initially regarded to be counter-intuitive as the initial pressure is a measured property. Numerous reviews have endorsed this methodology, which is now being used as a standard at Santos.

Rate Decline Curves Analysis of a Vertical Fractured Well With Fracture Face Damage

Rate decline analysis is a significant method for predicting well performance. Previous studies on rate decline analysis of fractured wells are all based on homogeneous reservoirs rather than homogeneous ones considering fracture face damage. In this article, a well model intercepted by a finite conductivity vertical fracture with fracture face damage is established to investigate how face damage factor affects the productivity of fractured well. Calculative results show that in transient flow, dimensionless rate decreases with the increase of fracture face damage and in pseudo steady-state flow, all curves under different face damage factors coincide with each other. Then, a new pseudo steady-state analytic formula and its validation are presented. Finally, new Blasingame type curves are established. It is shown that the existence of fracture damage would decrease the rate when time is relatively small, so fracture damage is an essential factor that we should consider for type curves analysis. Compared with traditional type curves, new type curves could solve the problem of both variable rate and variable pressure drop for fractured wells with fracture face damage factor. A gas reservoir example is performed to demonstrate the methodology of new type curves analysis and its validation for calculating important formation parameters.

Application of Decline Analysis in Fractured Reservoirs, Field Case Studies

Decline curve analysis has some advantages over transient well test analysis in which it is not required to shut-in the well and also wellbore storage effects do not exist. Few studies have been done on decline curve analysis of naturally fractured reservoirs but there are even some limitations with available models. On the other hand well test could be expensive and in some operational conditions shutting the well to obtain reservoir parameters is almost impossible. Therefore, investigating the applicability of homogenous reservoir decline models for production data analysis of naturally fractured reservoirs is necessary. In this paper the most important decline models have been used to evaluate reservoir parameters in three Iranian naturally fractured reservoirs and the results have been compared to transient well test analysis. A useful and applicable procedure is also introduced to correct the initial production data when they do not have necessary conditions. The results show that Agarwal-Gardner and Blasingame type curves predict acceptable values for permeability compared to transient well test analysis while Fetkovich type curve cannot predict accurate values. Determined skin values in all wells of the three studied reservoirs are negative. Negative values can be considered to be affected by existing fracture networks in the vicinity of producing wells and also periodic well stimulations. The results also show that Neglecting produced condensates of gas condensate reservoirs with Liquid-Gas Ratio (LGR) less than 100 bbl/MMscf cannot significantly affect decline curve analysis results.

Classification of carbonate gas condensate reservoirs using well test and production data analyses

Carbonate reservoir patterns play an important role in the production performance of oil and gas wells, and it is usually classified through static data analysis which cannot reflect the actual well performance. This paper takes the Tazhong No. 1 gas field in the Tarim Basin, China as an example to investigate the classification of carbonate reservoirs. The classification method mainly combines well test analysis with production analysis — especially the Blasingame type curve method. Based on the characteristics of type curves for well test analysis and the Blasingame method, the relationship between the type curves and reservoir pattern was established. More than 20 wells were analyzed and the reservoirs were classified into 3 major patterns with 7 sub-classes. Furthermore, the classification results were validated by dynamic performance analysis of wells in the Tazhong No.1 gas field. On the basis of the classification results, well stimulation (i.e. water flooding in a single well) was carried out in three volatile-oil wells, and the oil recovery increased by up to 20%.