Impact of Delayed Flowback on Well Performance: Case Study

2022 ◽  
Author(s):  
Ruqia Al Shidhani ◽  
Ahmed Al Shueili ◽  
Hussain Al Salmi ◽  
Musallam Jaboob
Keyword(s):  
Hydraulic Fracturing ◽  
Large Scale ◽  
Gas Permeability ◽  
Real Data ◽  
Formation Damage ◽  
Single Fracture ◽  
Well Performance ◽  
Fracture Conductivity ◽  
Wellhead Pressure ◽  
The Impact

Abstract Due to a resource optimization and efficiency improvements, wells that are hydraulically fractured in the tight gas Barik Formation of the Khazzan Field in the Sultanate of Oman are often temporarily left shut-in directly following a large scale massive hydraulic fracturing stimulation treatment. Extensive industry literature has often suggested (and reported), that this may result in a significant direct loss of productivity due to the delayed flowback and the resulting fracture conductivity and formation damage. This paper will review the available data from the Khazzan Field address these concerns; indicating where the concerns should and should not necessarily apply. The Barik Formation in the Khazzan Field is an over-pressured gas-condensate reservoir at 4,500 m with gas permeability ranging from 0.1 to 20 mD. The average well after hydraulic fracturing produces 25 MMscfd and 500 bcpd against a wellhead pressure of 4,000 psi. A typical hydraulic fracturing stimulation treatment consists of 14,000 bbl of a borate-crosslinked guar fluid, placing upwards of 1MM Lbs of high conductivity bauxite proppant within a single fracture. In order to assess the potential production loss due to delayed flowback operations, BP Oman performed a suite of formation damage tests including core samples from the Barik reservoir, fracture conductivity considerations and dynamic behaviors. Additionally, normalized production was compared between offset wells that were cleaned-up and put onto production at different times after the hydraulic fracturing operations. Core tests showed a range of fracture conductivities over time with delayed flowback after using the breaker concentrations from actual treatments. As expected, enhanced conductivity was achieved with additional breaker. The magnitude of the conductivity being created in these massive treatments was also demonstrated to be dominant with respect to damage effects. Finally, a normalized comparison of an extensive suite of wells clearly showed no discernible loss of production resulted from any delay in the flowback operations. This paper describes in details the workflow and resulting analysis of the impact of extensive shut-in versus immediate flowback post massive hydraulic fracturing. It indicates that the impact of such events will be limited if the appropriate steps have been taken to minimize the opportunity for damage to occur. Whereas the existing fracturing literature takes the safe stance of indicating that damage will always result from such shut-ins, this paper will demonstrate the limitations of such assumptions and the flexibility that can be demonstrated with real data.

Influence of Oriented Perforation Design on Refracture Reorientation: Simulation and Experiment

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Minhui Qi ◽  
Mingzhong Li ◽  
Tiankui Guo ◽  
Chunting Liu ◽  
Song Gao ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Large Scale ◽  
Simulation Models ◽  
Fracture Initiation ◽  
Simulation Method ◽  
Induced Stress ◽  
Study Results ◽  
Simulation Results ◽  
Fracturing Experiments ◽  
The Impact

The oriented perforating is the essential technique to guide the refracture reorientation, but the influence of the oriented perforation design on the refracture steering radius is still unclear. In this paper, the factors influencing the refracture reorientation were studied by simulation models and experiments. The effects of initial fracture, well production, and perforations on the refracture initiation and propagation were analyzed. Three-dimensional finite element models were conducted to quantify the impact of perforation depth, density, and azimuth on the refracture. The large-scale three-axis hydraulic fracturing experiments guided by oriented perforations were also carried out to verify the fracture initiation position and propagation pattern of the simulation results. The research results showed that perforations change the near-wellbore induced stress distribution, thus changing the steering radius of the refracture. According to the simulation results, the oriented perforation design has a significant influence on the perforation guidance effect and refracture characteristics. Five hydraulic fracturing experiments proved the influence of perforating parameters on fracture initiation and morphology, which have a right consistency between the simulation results. This paper presents a numerical simulation method for evaluating the influence of the refracture reorientation characteristics under the consideration of multiple prerefracturing induced-stress and put forward the oriented perforation field design suggestions according to the study results.

Development of Tight Upper Cretaceous Reservoir in Offshore Black Sea Adds Life to a Mature Asset

2021 ◽  
Author(s):  
I. Mitrea ◽  
R. Cataraiani ◽  
M. Banu ◽  
S. Shirzadi ◽  
W. Renkema ◽  
...  
Keyword(s):  
Black Sea ◽  
Upper Cretaceous ◽  
Rock Physics ◽  
Oil Production ◽  
Economic Life ◽  
Production Performance ◽  
Single Fracture ◽  
Well Performance ◽  
Acoustic Image ◽  
The Impact

Abstract This Upper Cretaceous reservoir, a tight reservoir dominated by silt, marl, argillaceous limestone and conglomerates in Black Sea Histria block, is the dominant of three oil-producing reservoirs in Histria Block. The other two, Albian and Eocene, are depleted, and not the focus of field re-development. This paper addresses the challenges and opportunities that were faced during the re-development process in this reservoir such as depletion, low productivity areas, lithology, seismic resolution, and stimulation effectiveness. Historically, production from Upper Cretaceous wells could not justify the economic life of the asset. As new fracturing technology evolved in recent years, the re-development focused on replacing old, vertical/deviated one-stage stimulations low producing wells with horizontal, multi-stage hydraulic fractured wells. The project team integrated various disciplines and approaches by re-processing old seismic to improve resolution and signal, integrating sedimentology studies using cores, XRF, XRD and thin section analysis with petrophysical evaluation and quantitative geophysical analyses, which then will provide properties for geological and geomechanical models to optimize well planning and fracture placement. Seven wells drilled since end of 2017 to mid-2021 have demonstrated the value of integration and proper planning in development of a mature field with existing depletion. Optimizing the well and fracture placement with respect to depletion in existing wells resulted in accessing areas with original reservoir pressure, not effectively drained by old wells. Integrating the well production performance with tracer results from each fractured stage, and NMR/Acoustic images from logs enhanced the understanding of the impact of lithofacies on stimulation. This has allowed better assessment and prediction of well performance, ultimately improving well placement and stimulation design. The example from this paper highlights the value of the integrating seismic reprocessing, attribute analysis, production technology, sedimentology, cuttings analysis and quantitative rock physics in characterizing the heterogeneity of the reservoir, which ultimately contributed to "sweet spot" targeting in a depleted reservoir with existing producers and deeper understanding of the development potential in Upper Cretaceous. The 2017-2021 wells contribute to more than 30 percent of the total oil production in the asset and reverse the decline in oil production. In addition, these wells have two to four times higher initial rates because of larger effective drainage area than a single fracture well. Three areas of novelty are highlighted in this paper. The application of acoustic image/NMR logging to identify lithofacies and optimize fracturing strategy in horizontal laterals. The tracers analysis of hydraulic fracture performance and integration with seismic and petrophysical analysis to categorize the productivity with rock types. The optimization of fracture placement considering the changes of fluid and proppant volumes without compromising fracture geometries and avoiding negative fracture driven interactions by customized pumping approach.

scholarly journals Quantile regression for challenging cases of eQTL mapping

2019 ◽  
Vol 21 (5) ◽  
pp. 1756-1765
Author(s):  
Bo Sun ◽  
Liang Chen
Keyword(s):  
Quantile Regression ◽  
Large Scale ◽  
High Throughput Sequencing ◽  
Linear Models ◽  
Real Data ◽  
Type I ◽  
Eqtl Mapping ◽  
Size Estimation ◽  
Rna Seq ◽  
The Impact

Abstract Mapping of expression quantitative trait loci (eQTLs) facilitates interpretation of the regulatory path from genetic variants to their associated disease or traits. High-throughput sequencing of RNA (RNA-seq) has expedited the exploration of these regulatory variants. However, eQTL mapping is usually confronted with the analysis challenges caused by overdispersion and excessive dropouts in RNA-seq. The heavy-tailed distribution of gene expression violates the assumption of Gaussian distributed errors in linear regression for eQTL detection, which results in increased Type I or Type II errors. Applying rank-based inverse normal transformation (INT) can make the expression values more normally distributed. However, INT causes information loss and leads to uninterpretable effect size estimation. After comprehensive examination of the impact from overdispersion and excessive dropouts, we propose to apply a robust model, quantile regression, to map eQTLs for genes with high degree of overdispersion or large number of dropouts. Simulation studies show that quantile regression has the desired robustness to outliers and dropouts, and it significantly improves eQTL mapping. From a real data analysis, the most significant eQTL discoveries differ between quantile regression and the conventional linear model. Such discrepancy becomes more prominent when the dropout effect or the overdispersion effect is large. All the results suggest that quantile regression provides more reliable and accurate eQTL mapping than conventional linear models. It deserves more attention for the large-scale eQTL mapping.

Comparison Between Dichotomous and Polytomous Scoring of Innovative Items in a Large-Scale Computerized Adaptive Test

2011 ◽  
Vol 72 (3) ◽  
pp. 493-509 ◽  
Author(s):  
Hong Jiao ◽  
Junhui Liu ◽  
Kathleen Haynie ◽  
Ada Woo ◽  
Jerry Gorham
Keyword(s):  
Large Scale ◽  
Credit Scoring ◽  
Real Data ◽  
Simulation Studies ◽  
Partial Credit ◽  
Ability Estimates ◽  
Operational Test ◽  
Dichotomous Scoring ◽  
Scoring Algorithms ◽  
The Impact

This study explored the impact of partial credit scoring of one type of innovative items (multiple-response items) in a computerized adaptive version of a large-scale licensure pretest and operational test settings. The impacts of partial credit scoring on the estimation of the ability parameters and classification decisions in operational test settings were explored in one real data analysis and two simulation studies when two different polytomous scoring algorithms, automated polytomous scoring and rater-generated polytomous scoring, were applied. For the real data analyses, the ability estimates from dichotomous and polytomous scoring were highly correlated; the classification consistency between different scoring algorithms was nearly perfect. Information distribution changed slightly in the operational item bank. In the two simulation studies comparing each polytomous scoring with dichotomous scoring, the ability estimates resulting from polytomous scoring had slightly higher measurement precision than those resulting from dichotomous scoring. The practical impact related to classification decision was minor because of the extremely small number of items that could be scored polytomously in this current study.

scholarly journals Evaluation Method of the Vertical Well Hydraulic Fracturing Effect Based on Production Data

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Debin Xia ◽  
Zhengming Yang ◽  
Daolun Li ◽  
Yapu Zhang ◽  
Ying He ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Optimization Design ◽  
Large Scale ◽  
Evaluation Method ◽  
Outer Region ◽  
Fracture Network ◽  
Single Fracture ◽  
Vertical Well ◽  
Cumulative Production ◽  
Volumetric Fracturing

Hydraulic fracturing technology has become a key technology for the development of low-permeability/tight oil and gas reservoirs. The evaluation on the postfracturing effect is imperative to the formulation and implementation of the fracturing and development plan. Based on the characteristics of the flow in fracture network after a large-scale hydraulic fracturing, a numerical method for evaluating the effect of fracturing in vertical well was established. This study conducts postfracturing effect evaluations to block C Oilfield’s wells that underwent conventional fracturing and volumetric fracturing, respectively, proposes the definition of fracture network conductivity and its relationship with cumulative production, and analyzes the fracturing construction parameters. The results suggest that the conventional fracturing can only form a single fracture instead of a stimulated reservoir volume (SRV) region. However, the volumetric fracturing transformation can form a complex fracture network system and SRV region and meanwhile bring obvious increase in the production. The effective time lasts for a longer period, and the increase of average daily oil is 2.2 times more than that of conventional fracturing. Additionally, with the progress of the production, the SRV area within the core region of the volume transformation gradually decreased from 6664.84 m2 to 4414.45 m2; the SRV area of the outer region decreased from 7913.5 m2 to 5391.3 m2. As the progress develops, the equivalent permeability and the area of the fracture gradually decrease as the fracturing effect gradually weakens, and so does the conductivity of the network decreasing exponentially; a good correlation is observed between the conductivity of the fracture network, the cumulative production, and fracturing construction parameters, which can serve as the evaluation parameters for the fracturing effects and the basis for fracturing productivity prediction and provide a guidance for fracturing optimization design.

scholarly journals FORMATION DAMAGE MECHANISMS AND NUMERICAL SIMULATION OF PERMEABILITY IMPAIRMENT IN HORIZONTAL WELLS

2021 ◽  
Vol 15 (2) ◽  
pp. 184-204
Author(s):  
Tunde Adeosun ◽  
Moruffdeen Adabanija ◽  
Folake Akinpelu
Keyword(s):  
Numerical Simulation ◽  
Linear Partial Differential Equation ◽  
Horizontal Wells ◽  
Numerical Approach ◽  
Formation Damage ◽  
Well Performance ◽  
Damage Mechanisms ◽  
Pressure Losses ◽  
Permeability Impairment ◽  
The Impact

Puzzling circumstance associated with formation damage near wellbore occur frequently, resulting in permeability impairments and increased pressure losses. Potential damage phenomenon usually starts from drilling to completion via production and such mechanisms have been fully considered. Most of the existing tasks to mitigate the near oil wellbore damages involve use of empirical models, conducting experiments, frequent shut down of wells for proper well tests and pressure maintenance are highly expensive and time consuming. Permeability impairments have been simulated by modifying Darcy’s equation to optimize reservoir pressure for improved near wellbore in horizontal wells. The model, transient linear partial differential equation (TLPDE) for impaired permeability is developed and numerically resolved using finite difference method. The model was implemented by writing codes in MATLAB language and the solution obtained was validated using synthetic/ field data. The results obtained for TLPDE model indicated pressure depletion over time. This was also shown for every values of coefficient of anisotropy until 400 days when the anisotropy became insignificant approaching isotropy condition, suggesting permeability impairment. Numerical simulation proved to be effective in simulating near oil wellbore damages. This paper describes the detailed mechanisms of formation damage and provided a numerical approach to model impaired permeability in horizontal wells. This approach allowed us to study the impact of various damage mechanisms related to drilling, completion conditions and significant improvement of near oil wellbore for well performance.

scholarly journals Dynamics of transposable element invasions with piRNA clusters

2018 ◽  
Author(s):  
Robert Kofler
Keyword(s):  
Drosophila Melanogaster ◽  
Equilibrium State ◽  
Transposable Element ◽  
Negative Selection ◽  
Large Scale ◽  
Real Data ◽  
Copy Numbers ◽  
Pirna Cluster ◽  
The Impact ◽  
Random Insertion

AbstractIn mammals and in invertebrates the proliferation of a newly invading transposable element (TE) is thought to be stopped by a random insertion of one member of the invading TE family into a piRNA cluster. This view is known as the trap model. Here we explore the dynamics of TE invasions under the trap model using large-scale computer simulations. We found that piRNA clusters confer a substantial benefit, effectively preventing extinction of host populations from an uncontrollable proliferation of deleterious TEs. We show that TE invasions under the trap model consists of three distinct phases: first the TE rapidly amplifies within the population, next TE proliferation is stopped by segregating cluster insertions and finally the TE is permanently inactivated by fixation of a cluster insertion. Suppression by segregating cluster insertions is unstable and bursts of TE activity may yet occur. The transpositon rate and the population size mostly influence the length of the phases but not the amount of TEs accumulating during an invasion. Solely the size of piRNA clusters was identified as a major factor influencing TE abundance. Investigating the impact of different cluster architectures we found that a single non-recombining cluster (e.g. the somatic cluster flamenco in Drosophila) is more efficient in stopping invasions than clusters distributed over several chromosomes (e.g germline cluster in Drosophila). With the somatic architecture fewer TEs accumulate during an invasion and fewer cluster insertions are required to stop the TE. The inefficiency of the germline architecture stems from recombination among cluster sites which makes it necessary that each diploid carries, on the average, four cluster insertions, such that most individuals will end up with at least one cluster insertion. Surprisingly we found that negative selection in a model with piRNA clusters can lead to a novel equilibrium state, where TE copy numbers remain stable despite only some individuals in a population carrying a cluster insertion. Finally when applying our approach to real data from Drosophila melanogaster we found that the trap model reasonably well accounts for the abundance of germline TEs but not of somatic TEs. The abundance of somatic TEs, such as gypsy, is much lower than expected.

The Geometry of a Large-Scale Nitrogen Gas Hydraulic Fracture Formed in Devonian Shale: An Example of Fracture Mapping With Tiltmeters

1982 ◽  
Vol 22 (05) ◽  
pp. 755-763 ◽  
Author(s):  
Keith Evans ◽  
Gary Holzhausen ◽  
D.M. Wood
Keyword(s):  
Hydraulic Fracturing ◽  
Large Scale ◽  
Nitrogen Gas ◽  
Hydraulic Stimulation ◽  
Wellhead Pressure ◽  
Fracture Development ◽  
Devonian Shale ◽  
Lineament Analysis ◽  
Fracture Mapping ◽  
Diagnostic Technologies

Abstract Ground deformations occurring around a well undergoing hydraulic fracturing stimulation are analyzed to obtain a description of the geometry and the development of the resulting fracture. Significant upward and lateral growth of a near-vertical fracture aligned with the proposed direction of maximum tectonic compression is inferred to take place initially. However, after six-tenths a the nitrogen gas fracturing fluid had been injected, fracture growth in a horizontal plane abruptly began, and vertical growth ceased. No indication of this breakout is evident in the wellhead pressure or flow rate records. The state of stress in the vicinity of the well is estimated and implications of the inferred fracture development behavior are discussed. Introduction Production enhancement of gas from wells draining low-permeability formations such as the Devonian shale series of the eastern U.S. commonly is attempted by use of hydraulic fracturing. The problem of designing such fractures to optimize the resulting yield has underlined the need for a more thorough understanding of the fracture process. To this end, several wells penetrating Devonian shale have been selected for intensive study during the fracturing treatments. The studies involve application of a wide variety of diagnostic technologies capable of supplying information pertinent to establishing the behavior of the fracture during the treatment and the principal factors that influence this behavior. This paper presents the results of applying the tiltmeter technique of fracture mapping to determine geometrical characteristics of the fracture resulting from injection of nitrogen gas into the 335 m (1,100 ft) deep Black No. 1 well, which penetrates the Devonian shale in Knox County, OH (Fig. 1). During treatment, which lasted from 16:47 to 17:15 hours (local time) on Oct. 22, 1979, a total of 2.59 × 104 std m3 (9.68 × 105 scf) of nitrogen gas at a wellhead temperature of 46 deg. C (115 deg. F) and pressure of 9.0 MPa (1.300 psi) was administered to the well. No proppant was used. The well was offered to the research program by its owners after production had declined from an initial 8.6 × 102 std m3/d (3.2 × 104 scf ft/D) after drilling in 1975 to essentially zero by the end of 1977. During this period of production, the well was openhole for the entire Devonian shale section (Fig. 2) and had suffered neither explosive nor hydraulic stimulation treatments. It is not known whether the bulk of production came from the shale matrix or from sets of high-angle natural fractures that intersected the well. Before the experiment, the well was recased as shown in Fig. 2. Other diagnostic technologies involved in the stimulation experiment included borehole seisviewer imagery, extensive logging and coring, lineament analysis, downhole television, nitrogen analysis, and a downhole three-component geophone systems which, like the tiltmeter array, was operated continuously throughout the treatment period. The results of these analyses are cited freely to support the interpretation presented. Theory The underlying principle of the tiltmeter technique is to determine the deformation field at the earth's surface that results from growth of the fracture structure at depth. SPEJ P. 755^

scholarly journals Fracturing Fluids and Their Application in the Republic of Croatia

2021 ◽  
Vol 11 (6) ◽  
pp. 2807
Author(s):  
Nediljka Gaurina-Međimurec ◽  
Vladislav Brkić ◽  
Matko Topolovec ◽  
Petar Mijić
Keyword(s):  
Hydraulic Fracturing ◽  
Gas Production ◽  
Well Performance ◽  
Fracturing Fluid ◽  
Wellhead Pressure ◽  
Well Production ◽  
Main Requirement ◽  
Fracturing Fluids ◽  
Fluid Properties ◽  
The Republic

Hydraulic fracturing operations are performed to enhance well performance and to achieve economic success from improved production rates and the ultimate reserve recovery. To achieve these goals, fracturing fluid is pumped into the well at rates and pressures that result in the creation of a hydraulic fracture. Fracturing fluid selection presents the main requirement for the successful performance of hydraulic fracturing. The selected fracturing fluid should create a fracture with sufficient width and length for proppant placement and should carry the proppant from the surface to the created fracture. To accomplish all those demands, additives are added in fluids to adjust their properties. This paper describes the classification of fracturing fluids, additives for the adjustment of fluid properties and the requirements for fluid selection. Furthermore, laboratory tests of fracturing fluid, fracture stimulation design steps are presented in the paper, as well as a few examples of fracturing fluids used in Croatia with case studies and finally, hydraulic fracturing performance and post-frac well production results. The total gas production was increased by 43% and condensate production by 106% in selected wells including wellhead pressure, which allowed for a longer production well life.

scholarly journals When tension is just a fluctuation

2021 ◽  
Vol 647 ◽  
pp. L5
Author(s):  
B. Joachimi ◽  
F. Köhlinger ◽  
W. Handley ◽  
P. Lemos
Keyword(s):  
Large Scale ◽  
Model Comparison ◽  
Bayes Factor ◽  
Computational Cost ◽  
Real Data ◽  
Microwave Background ◽  
Order Unity ◽  
Physical Experiments ◽  
Bayesian Evidence ◽  
The Impact

Summary statistics of likelihood, such as Bayesian evidence, offer a principled way of comparing models and assessing tension between, or within, the results of physical experiments. Noisy realisations of the data induce scatter in these model comparison statistics. For a realistic case of cosmological inference from large-scale structure, we show that the logarithm of the Bayes factor attains scatter of order unity, increasing significantly with stronger tension between the models under comparison. We develop an approximate procedure that quantifies the sampling distribution of the evidence at a small additional computational cost and apply it to real data to demonstrate the impact of the scatter, which acts to reduce the significance of any model discrepancies. Data compression is highlighted as a potential avenue to suppressing noise in the evidence to negligible levels, with a proof of concept demonstrated using Planck cosmic microwave background data.

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