Importance of Fracture Geometry and Conductivity in Improving Efficiency of Acid Fracturing in Carbonates

Newman,; Pavloudis, M.; Rahman, Md. Motiur

doi:10.2118/2009-146

Canadian International Petroleum Conference 2009

DOI: 10.2118/2009-146

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Importance of Fracture Geometry and Conductivity in Improving Efficiency of Acid Fracturing in Carbonates

Newman Newman

M. Pavloudis

Md. Motiur Rahman

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Cited by 8 publications

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“…The reaction rate of HCl-dolomite is surface-transfer limited, as the reaction rate of the acid on the exposed rock face is the limiting reaction. The reaction between dolomite-HCl is also more sensitive to temperature than the HCl-calcite reaction (Newman et al, 2009). These differences in reaction are due to the tighter packing structure of dolomite as compared to calcite (Gomaa and Nasr-El-Din, 2009) and the stronger bond between oxygen and magnesium in dolomite due to higher Van…”

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Acid Fracturing Carbonate-Rich Shale: A Feasibility Investigation of Eagle Ford Formation

Cash

Zhu

Hill

2016

Day 3 Fri, August 26, 2016

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Due to the extensive technically recoverable shale natural gas resources and an increase in production from shale plays over the last 10 years, it is essential to focus on stimulation techniques to enhance productivity in shale resources. One such stimulation technique is acid fracturing. Similar to hydraulic fracturing, acid fracturing injects acid into a formation at a pressure greater than the fracture pressure, creating fractures and etching the created fracture face. The high carbonate content of the Eagle Ford Shale makes the formation a possible acid fracturing candidate. Minimal research has been completed on the effects of acid fracturing high carbonate-containing shale formations, where various conditions can limit the permeability of petroleum fluids. In this study, eight Eagle Ford shale samples, four from Zone C and four from Zone D, are used to determine the effect of surface etching pattern, acid concentration, calcite content, and Brinell Hardness Number on created acid fracture conductivity in the Eagle Ford shale. The resultant surface etching volume is determined by a pre-and post-surface Profilometer scan to calculate the change in surface profile. Calcite content is determined by X-Ray Diffraction analyses. Conductivity tests are performed on the eight samples up to a closure stress of 4000 psi, sample integrity permitting. Based on the results determined in this study, acid fracturing the Eagle Ford shale could provide optimistic increases in production. Acid fracturing treatments in high calcite containing zones of the Eagle Ford shale are expected to result in an increase in productivity. For the Eagle Ford Shale, the surface etching patterns that result in iii highly sustained conductivity values are channeling and roughness. A direct correlation is shown between calcite content of the shale and resultant surface etching volume. Furthermore, the higher the calcite content of the samples, the more likely the etching pattern will result in channeling and surface roughness. Brinell Hardness tests are completed on Eagle Ford samples determining that, on average, the higher the Brinell Hardness number, the better resulting surface etching pattern and sustained acid fracture conductivity.iv

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mentioning

confidence: 99%

Acid Fracturing Carbonate-Rich Shale: A Feasibility Investigation of Eagle Ford Formation

Cash

Zhu

Hill

2016

Day 3 Fri, August 26, 2016

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Study of 2-D and 3-D Hydraulic Fractures with Non-Uniform Conductivity and Geometry Using Source and Sink Function Methods

Xiao

Zhao

2012

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During hydraulic fracturing process, different hydraulic loading and stress status of formations result in hydraulic fractures with various geometries and properties. Several propagation models including PKN and KGD have been widely applied in fracturing design and implementation. However, in the process of post-stimulation modeling, fractures are usually simplified with uniform geometries and conductivity distribution; therefore the effects of actual fracture geometry and proppant properties on the well transient pressure and production performance remain unclear. This study intends to comprehensively study the fractured wells with 2-D and 3-D non-uniform geometry and conductivity distribution. In the development of shale gas reservoirs and tight oil formations, horizontal well multistage fracturing is the key technology. The modeling results presented in this paper can help offer valuable information of reservoir properties, evaluate the conductivity distribution of propped fractures, simulate more realistic fracture configurations, and help optimize fracture treatment process and fractured wells’ performances with improved accuracy. A semi-analytical approach coupling fluid flow in reservoir and fractures existed in more realistic shape with non-uniform conductivity distribution has been developed to obtain well transient pressure and production responses. Source and sink function method is utilized to solve unsteady state flow problems of fluid flowing from reservoir to non-uniform fractures with geometries that are well defined in PKN, KGD and other generally ideal models. The effect of fracture conductivity with linear and stepwise distribution, and elliptic fracture shape variations has been investigated. Comparison study has been highlighted to illustrate effects of fracture geometry and conductivity distributions. Realistic hydraulic fractured wells with non-uniform fracture geometry and conductivity have been studied to showcase a consistent workflow of entering fracture properties from hydraulic fracturing models and outputting fractured well performance prediction in post-stimulation reservoirs. Instead of assuming pseudo-steady state flow status between reservoir and fracture, unsteady state flow problems related to non-uniform fracture geometric have been solved in a semi-analytical manner with solution of near analytical accuracy. More realistic fracture geometries estimated from fracture propagation models can be entered into post-stimulation models without idealized simplification; thus the gap between fracture propagation and post-stimulation modeling has been fulfilled.

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First Acid Fracturing Unlocks the Production Potential of Tight Tuba Carbonate Reservoir, North Kuwait

et al. 2015

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Upcoming Reservoirs in North Kuwait will play significant role for meeting NK’s strategic production target. Recent full field study of Sabryia Tuba carbonate reservoir makes it the largest Oil in-Place of the Upcoming Reservoirs in NK. Sabriyah Tuba, though discovered in the 60’s, is still relatively under exploited presently with only 13 active wells with very low total production rate compared to other reservoirs. High reservoir heterogeneity, tightness and poor fluid properties necessitate the application of new stimulation technology targeting good frac conductivity and deep penetration for effective productivity and recovery enhancement. With efforts of a multidisciplinary team, new acid frac fluid, diverter and high leak off control technologies have been designed and executed successfully in two stages covering multiple reservoir layers for the first time in Tuba. Tuba is tight multilayer limestone reservoir. Owing to the low reservoir transmissibility, even low average well production assisted by Artificial Lift causes near-wellbore (not regional) rapid decline in pressure. Full-scale commercial exploitation of the Tuba reservoir therefore requires advanced technologies for productivity enhancement. The well under study is vertical, drilled in 2012 and completed in Upper and Lower Tuba with conventional matrix acid stimulation which had a very steep post-treatment decline rate. It was selected for first application of acid fracturing due to its excellent reservoir development in higher structure position with high initial pressure and medium oil quality, but low production rate. The job was designed to implement a 3-stage acid frac. The first stage was successfully executed. The second and third stages were combined into one stage due to the vertical communication between all 4 Upper Tuba layers during the data fracture treatment. Many technical and operational challenges were faced and properly handled through integrated communication between different participating teams with lessons learned are to be considered in next designs and executions. Post acid Frac, a production log (PLT) was recorded and showed greater contribution from the Upper Tuba intervals. The well has been monitored closely where stabilization was observed in short time period represented in stabilized Pump Intake pressure and production rate that has been tripled post stimulation with an estimated reservoir productivity improvement of about ~3 folds from nodal analysis. The positive result of first acid frac reinforces the action plan to proceed with such stimulation technology. It is expected that the oil gain potential will be significantly more in horizontal completions. Therefore, acid frac stimulation for 2 Horizontal Tuba’s wells is under study. The success of such application will formulate the drilling, completion and stimulation development strategy for the entire Tuba reservoir including early stimulation to improve initial productivity that will contribute significantly to the NK production target. This paper describes the design, implementation and production impact of an advanced fiber based acid fracturing treatment that was successfully executed across the cased-hole of a pilot vertical well that is shaping the production enhancement strategy for Sabriya’s Tuba tight reservoir in North Kuwait field. The paper also focuses on the acid fracturing technique that delivers hydraulic acid fractures with deep, infinitely conductive channel compared to conventional acid stimulation techniques previously employed and their immense impact on production.

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Importance of Fracture Geometry and Conductivity in Improving Efficiency of Acid Fracturing in Carbonates

Cited by 8 publications

References 0 publications

Acid Fracturing Carbonate-Rich Shale: A Feasibility Investigation of Eagle Ford Formation

Acid Fracturing Carbonate-Rich Shale: A Feasibility Investigation of Eagle Ford Formation

Study of 2-D and 3-D Hydraulic Fractures with Non-Uniform Conductivity and Geometry Using Source and Sink Function Methods

First Acid Fracturing Unlocks the Production Potential of Tight Tuba Carbonate Reservoir, North Kuwait

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