scholarly journals Interaction Law between Natural Fractures-Vugs and Acid-Etched Fracture during Steering Acid Fracturing in Carbonate Reservoirs

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Yifan Dai ◽  
Bing Hou ◽  
Changlin Zhou ◽  
Kunpeng Zhang ◽  
Fei Liu
Keyword(s):  
Fracture Surface ◽  
Physical Simulation ◽  
Carbonate Reservoir ◽  
Natural Fracture ◽  
Simulation Experiments ◽  
True Triaxial ◽  
Acid Fracturing ◽  
Low Viscosity ◽  
Fracturing Experiments ◽  
Interaction Law

Steering acid fracturing is a technique that improves the conductivity of carbonate reservoir. It is widely used in a carbonate reservoir. However, due to the lack of comparative experiments, the application of steering acid to improve the fracturing results is still unknown. Therefore, a series of true triaxial acid fracturing experiments were conducted to study steering acid fracturing in carbonate reservoir. The carbonate specimens used in the experiment were from the Qixia group and Dengsi Member in Sichuan, China. In this study, slick water, cross-linked gel, and self-generating acid were used as ahead fluid to cooperate with steering acid. Experimental results show that (1) the low-viscosity ahead fluid with steering acid can result in more complex fractures; (2) the complexity of fractures is influenced by natural fracture and the viscosity of the ahead fluid; and (3) based on the 3D scanning results of the fracture surface, different ahead fluids will lead to different corrosion results. This study provides useful suggestions on steering acid fracturing design and physical simulation experiments.

Flow-induced microfracturing of granite in superhot geothermal environments

2021 ◽  
Author(s):  
Ryota Goto ◽  
Noriaki Watanabe ◽  
Kiyotoshi Sakaguchi ◽  
Youqing Chen ◽  
Takuya Ishibashi ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Working Fluid ◽  
Fracture System ◽  
Geothermal Resources ◽  
Rock Body ◽  
True Triaxial ◽  
Low Viscosity ◽  
Fracture Systems ◽  
Geothermal Environments ◽  
Fracturing Experiments

<p>Superhot geothermal environments with temperatures of approximately 400-500<sup>︒</sup>C at depth of approximately 2-4 km are expected as a new geothermal energy frontier. In order to efficiently exploit the superhot geothermal resources, fracture systems are necessary as flow path of working fluid. Hydraulic fracturing is a promising technique because it is able to create a new fracture system or enhance the permeability of preexisting fracture system. Laboratory-scale hydraulic fracturing experiments of granite have demonstrated the formation of densely distributed network of permeable fractures throughout the entire rock body at or near the supercritical temperature for water. Though the process has been presumed to involve continuous infiltration of low-viscosity water into preexisting microfractures followed by creation and merger of the subsequent fractures, plausible criterion for the fracturing is yet to be clarified. The possibility that the Griffith failure criterion is available to predict the occurrence of fracturing was shown by hydraulic fracturing experiments with acoustic emission measurements of granite at 400<sup>︒</sup>C under true triaxial stress. The present study provides a theoretical basis required to establish the procedure for hydraulic fracturing in superhot geothermal environment.</p>

Modeling Acid Fracturing Treatments with Multi-Stage Alternating Injection of Pad and Acid Fluids

2021 ◽  
Author(s):  
Rencheng Dong ◽  
Mary F. Wheeler ◽  
Hang Su ◽  
Kang Ma
Keyword(s):  
Viscous Fingering ◽  
High Viscosity ◽  
Carbonate Reservoirs ◽  
Acid Etching ◽  
Fracture Geometry ◽  
Fracture Conductivity ◽  
Acid Fracturing ◽  
Fracture Surfaces ◽  
Low Viscosity ◽  
Multi Stage

Abstract Acid fracturing technique is widely applied to stimulate the productivity of carbonate reservoirs. The acid-fracture conductivity is created by non-uniform acid etching on fracture surfaces. Heterogeneous mineral distribution of carbonate reservoirs can lead to non-uniform acid etching during acid fracturing treatments. In addition, the non-uniform acid etching can be enhanced by the viscous fingering mechanism. For low-perm carbonate reservoirs, by multi-stage alternating injection of a low-viscosity acid and a high-viscosity polymer pad fluid during acid fracturing, the acid tends to form viscous fingers and etch fracture surfaces non-uniformly. To accurately predict the acid-fracture conductivity, this paper developed a 3D acid fracturing model to compute the rough acid fracture geometry induced by multi-stage alternating injection of pad and acid fluids. Based on the developed numerical simulator, we investigated the effects of viscous fingering, perforation design and stage period on the acid etching process. Compared with single-stage acid injection, multi-stage alternating injection of pad and acid fluids leads to narrower and longer acid-etched channels.

Using Advance Acid Fracturing Design to Increase the Production Efficiency in a HPHT Reservoir: A Success Story from Southern Mexico

2021 ◽  
Author(s):  
Frank Figueroa ◽  
Gustavo Mejías ◽  
José Frías ◽  
Bonifacio Brito ◽  
Diana Velázquez ◽  
...  
Keyword(s):  
High Temperature ◽  
Laboratory Tests ◽  
Reaction Rates ◽  
Gas Production ◽  
Carbonate Reservoir ◽  
Fluid Distribution ◽  
Acid Etching ◽  
Southern Mexico ◽  
Acid Fracturing ◽  
Fluid Systems

Abstract Enhanced hydrocarbon production in a high-pressure/high-temperature (HP/HT) carbonate reservoir, involves generating highly conductive channels using efficient diversion techniques and custom-designed acid-based fluid systems. Advanced stimulation design includes injection of different reactive fluids, which involves challenges associated with controlling fluid leak-off, implementing optimal diversion techniques, controlling acid reaction rates to withstand high-temperature conditions, and designing appropriate pumping schedules to increase well productivity and sustainability of its production through efficient acid etching and uniform fluid distribution in the pay zone. Laboratory tests such as rock mineralogy, acid etching on core samples and solubility tests on formation cuttings were performed to confirm rock dissolving capability, and to identify stimulation fluids that could generate optimal fracture lengths and maximus etching in the zone of interest while corrosion test was run to ensure corrosion control at HT conditions. After analyzing laboratory tests results, acid fluid systems were selected together with a self-crosslinking acid system for its diversion properties. In addition, customized pumping schedule was constructed using acid fracturing and diverting simulators and based on optimal conductivity/productivity results fluid stages number and sequence, flow rates and acid volumes were selected. The engineered acid treatment generated a network of conductive fractures that resulted in a significant improvement over initial production rate. Diverting agent efficiency was observed during pumping treatment by a 1,300 psi increase in surface pressures when the diverting agent entered the formation. Oil production increased from 648.7 to 3105.89 BPD, and gas production increased from 4.9 to 26.92 MMSCFD. This success results demonstrates that engineering design coupled with laboratory tailor fluids designs, integrated with a flawless execution, are the key to a successful stimulation. This paper describes the details of acidizing technique, treatment design and lessons learned during execution and results.

scholarly journals An innovative concept on deep carbonate reservoir stimulation: Three-dimensional acid fracturing technology

2020 ◽  
Vol 7 (5) ◽  
pp. 484-497
Author(s):  
Jianchun Guo ◽  
Bo Gou ◽  
Nan Qin ◽  
Junsheng Zhao ◽  
Lin Wu ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Carbonate Reservoir ◽  
Acid Fracturing ◽  
Reservoir Stimulation ◽  
Innovative Concept

An Integrated Experimental Method to Investigate Tool-Less Temporary-Plugging Multistage Acid Fracturing of Horizontal Well by Using Self-Degradable Diverters

SPE Journal ◽  
2020 ◽  
Vol 25 (03) ◽  
pp. 1204-1219 ◽  
Author(s):  
Lufeng Zhang ◽  
Fujian Zhou ◽  
Jianye Mou ◽  
Wei Feng ◽  
Zhun Li ◽  
...  
Keyword(s):  
Fracture Surface ◽  
Evaluation System ◽  
Horizontal Well ◽  
Single Type ◽  
Fracture Width ◽  
Acid Fracturing ◽  
Integrated Method ◽  
Tight Carbonate ◽  
Operation Cost ◽  
Insight Into

Summary Tool-less temporary-plugging multistage acid fracturing of horizontal well is a necessary technology to unlock the production potential and enable commercial productivity for tight carbonate reservoirs. However, this technique has not been investigated experimentally yet, and the plugging behavior of diverters within acid-etched fracture is still unclear. In this paper, we propose an integrated method to experimentally study tool-less multistage fracturing with diverters. First, we introduce an innovative 3D printing method to reproduce the roughness of acid-etched fracture surface and design an acid-etched fracture temporary plugging evaluation system to satisfy the requirements of temporary plugging experiments. Then, we conduct a series of plugging experiments to optimize the diverter's formula for creating a tight plugging zone within an acid-etched fracture under different fracture widths. On the basis of the description of the fracture surface, we further analyze the formation process and mechanism of temporary plugging. Finally, we further verify through laboratory experiments using a modified true tri-axial fracturing system the feasibility of using a single type of diverter and combined diverters to achieve tool-less temporary plugging staged fracturing of horizontal well. The experimental results show the following findings: (1) Pure fibers can realize temporary plugging at lower fracture width (≤2 mm). (2) To achieve temporary plugging, the diameter of particulates should not be less than half of the fracture width under the condition of larger fracture width (≥4 mm). (3) The fracture surface morphology affects the formation time of temporary plugging, but does not affect whether temporary plugging is formed or not. (4) Using a steel plate with a smooth fracture surface to conduct optimization experiments will increase the dosage of diverters, thus increasing the operation cost. (5) Pure particulates cannot achieve favorable plugging effect. This study provides an insight into multistage acid fracturing.

Acid Fracture Conductivity Behavior of Tahe Carbonate: High Closure Stress, Long-Term Conductivity, and Composite Conductivity

2014 ◽  
Vol 1042 ◽  
pp. 44-51
Author(s):  
Jia Nye Mou ◽  
Mao Tang Yao ◽  
Ke Xiang Zheng
Keyword(s):  
Creep Deformation ◽  
Contact Time ◽  
Carbonate Reservoir ◽  
Fracture Conductivity ◽  
Acid Rock ◽  
Acid Fracturing ◽  
Closure Stress ◽  
Composite Conductivity ◽  
Conductivity Behavior

Acid fracture conductivity is a key parameter in acid fracturing designs and production performance prediction. It depends on the fracture surface etching pattern, rock mechanical properties, and closure stress. The fracture surfaces undergo creep deformation under closure stress during production. Preservation of fracture conductivity becomes a challenge at elevated closure stress. In this paper, we investigated acid fracture conductivity behavior of Tahe deep carbonate reservoir with high closure stress and high temperature. A series of acid fracture conductivity experiment was conducted in a laboratory facility designed to perform acid fracture conductivity. Gelled acid and cross linked acid with different acid-rock contact times were tested for analyzing the effect of acid type and acid-rock contact time on the resulting conductivity. Closure stress up to 100MPa was tested to verify the feasibility of acid fracturing for elevated closure stress. Long-term conductivity up to 7-day was tested to determine the capability of conductivity retaining after creep deformation. Composite conductivity of acid fracture with prop pant was also carried out. The study shows that the fracture retained enough conductivity even under effective closure stress of 70MPa. The gelled acid has a much higher conductivity than the cross linked acid for the same contact time. For the gelled acid, contact time above 60-minute does not lead to conductivity increase. Acid fracture with prop pant has a lower conductivity at low closure stress and a higher conductivity at high closure stress than the acid fracture, which shows composite conductivity is a feasible way to raise conductivity at high closure stress. The long-term conductivity tests show that the acid fracture conductivity decreases fast within the first 48-hour and then levels off. The conductivity keeps stable after 120-hour. An acid fracture conductivity correlation was also developed for this reservoir.

Some challenges in hydraulic fracturing of tight gas reservoirs: an experimental study

2011 ◽  
Vol 51 (1) ◽  
pp. 499 ◽  
Author(s):  
Vamegh Rasouli ◽  
Mohammad Sarmadivaleh ◽  
Amin Nabipour
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Oil And Gas ◽  
Interaction Mechanism ◽  
Natural Fracture ◽  
Gas Reservoirs ◽  
Tight Sandstone ◽  
True Triaxial ◽  
Rock Types ◽  
Interface Parameters

Hydraulic fracturing is a technique used to enhance production from low quality oil and gas reservoirs. This approach is the key technique specifically in developing unconventional reservoirs, such as tight formations and shale gas. During its propagation, the hydraulic fracture may arrive at different interfaces. The mechanical properties and bounding quality of the interface as well as insitu stresses are among the most significant parameters that determine the interaction mechanism, i.e. whether the hydraulic fracture stops, crosses or experiences an offset upon its arrival at the interface. The interface could be a natural fracture, an interbed, layering or any other weakness feature. In addition to the interface parameters, the rock types of the two sides of the interface may affect the interaction mechanism. To study the interaction mechanism, hydraulic fracturing experiments were conducted using a true triaxial stress cell on two cube samples of 15 cm. Sample I had a sandstone block in the middle surrounded by mortar, whereas in sample II the location of mortar and tight sandstone blocks were changed. The results indicated that besides the effect of the far field stress magnitudes, the heterogeneity of the formation texture and interface properties can have a dominant effect in propagation characteristics of an induced fracture.

scholarly journals A rock self-supporting high conductivity acid fracturing technique in a deep carbonate reservoir

2020 ◽  
Vol 570 ◽  
pp. 022005
Author(s):  
Lu Baoping ◽  
Jun Zhou ◽  
Tingxue Jiang ◽  
Shidong Ding ◽  
Linbo Zhou ◽  
...  
Keyword(s):  
Carbonate Reservoir ◽  
High Conductivity ◽  
Acid Fracturing

The transformation effect of source rock-derived acidic fluid on carbonate reservoir from simulation experiments

2020 ◽  
Author(s):  
Qian Ding ◽  
Zhiliang He ◽  
Dongya Zhu
Keyword(s):  
Physical Properties ◽  
Source Rock ◽  
Carbonate Reservoir ◽  
Carbonate Reservoirs ◽  
Source Rocks ◽  
Petroleum Exploration ◽  
Hydrocarbon Generation ◽  
High Quality ◽  
Simulation Experiments ◽  
Deep Layers

<p>Deep and ultra-deep carbonate reservoir is an important area of petroleum exploration. However, the prerequisite for predicting high quality deep ultra-deep carbonate reservoirs lays on the mechanism of carbonate dissolution/precipitation. It is optimal to perform hydrocarbon generation-dissolution simulation experiments to clarify if burial dissolution could improve the physical properties of carbonate reservoirs, while quantitatively and qualitatively describe the co-evolution process of source rock and carbonate reservoirs in deep layers. In this study, a series of experiments were conducted with the limestone from the Ordovician Yingshan Formation in the Tarim Basin, and the low maturity source rock from Yunnan Luquan, with a self-designed hydrocarbon generation-dissolution simulation equipment. The controlling factors accounted for the alteration of carbonate reservoirs and dissolution modification process by hydrocarbon cracking fluid under deep burial environments were investigated by petrographic and geochemical analytical methods. In the meantime, the transformation mechanism of surrounding rocks in carbonate reservoirs during hydrocarbon generation process of source rock was explored. The results showed that: in the burial stage, organic acid, CO<sub>2</sub> and other acidic fluids associated with thermal evolution of deep source rocks could dissolve carbonate reservoirs, expand pore space, and improve porosity. Dissolution would decrease with the increasing burial depth. Whether the fluid could improve reservoir physical properties largely depends on calcium carbonate saturation, fluid velocity, water/rock ratio, original pore structure etc. This study could further contribute to the prediction of high-quality carbonate reservoirs in deep and ultra-deep layers.</p>

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