From Matrix Acidizing to Acid Fracturing: A Laboratory Evaluation of Acid/Rock Interactions

2001 ◽  
Vol 16 (01) ◽  
pp. 22-29 ◽  
Author(s):  
B. Bazin
Keyword(s):  
Laboratory Evaluation ◽  
Acid Rock ◽  
Matrix Acidizing ◽  
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.

Decision Criterion for Acid Stimulation Method in Carbonate Reservoirs: Matrix Acidizing or Acid Fracturing?

2020 ◽  
Author(s):  
Mateus Palharini Schwalbert ◽  
Murtada Saleh Aljawad ◽  
Alfred Daniel Hill ◽  
Ding Zhu
Keyword(s):  
Decision Criterion ◽  
Carbonate Reservoirs ◽  
Matrix Acidizing ◽  
Acid Fracturing ◽  
Stimulation Method

Characteristics of Acid Reaction in Limestone Formations

1971 ◽  
Vol 11 (04) ◽  
pp. 406-418 ◽  
Author(s):  
D.E. Nierode ◽  
B.B. Williams
Keyword(s):  
Transfer Rate ◽  
Reaction Rate ◽  
Mass Transfer Rate ◽  
Field Conditions ◽  
Rock Surface ◽  
Fluid Loss ◽  
Matrix Acidizing ◽  
Acid Fracturing ◽  
Acid Reaction ◽  
Flow Through

Abstract A kinetic model for the reaction of Hydrochloric acid with limestone bas been determined. Reaction order and rate constant for this model were calculated from experiments where acid reacted with a single calcium carbonate plate. Experiments were performed so that acid flow past the plate and mass transfer rate to the rock surface could be calculated theoretically. The resulting model, therefore, accurately represents the acid reaction process at the rock surface and is independent of mass transfer rate. Combination of this model with existing theory allows prediction of acid reaction during acid fracturing operations. A model for acid reaction in wormholes created during matrix acidization treatments is presented along with data for reaction of hydrochloric, formic and acetic acids in a wormhole. Factors limiting stimulation in acid fracturing or matrix acidizing treatments are then discussed. Introduction To predict the stimulation ratio resulting from acid fracturing or matrix acidizing treatments it is necessary to know the rate of acid reaction under field conditions. In acid fracturing treatments, for example, reaction occurs as acid flows through a narrow fracture. Reaction in a matrix treatment occurs during flow through wormholes (channels of roughly circular cross-section) created by acid reaction. In both treatments, a large amount of mixing occurs during flow through the fracture or channel as a result of tortuosity and wall roughness. Reaction rate can be obtained from experiments, or predicted by theoretical calculations that accurately model field conditions. In general a theoretical procedure is preferred since it can be used without recourse to laboratory testing. Acid-reaction-rate data have been reported from a number of experiments intended to simulate acid reaction in field treatments. Tests most often used are:the static reaction rate test, in which a cube of limestone is contacted with unstirred acid at a known ratio of rock surface area to acid volume;flow experiments, where acid is forced to flow between parallel plates of limestone; anddynamic tests, whine limestone specimens are rotated through an agitated acid solution. In general, these tests model some aspects of the reaction process, such as area to volume ratio, or acid flow velocity, but do not accurately model all field conditions. To obtain an accurate mathematical model for field treatments, assuming fracture or wormhole geometry is known, it is necessary to characterize acid reaction kinetics at the limestone surface, rate of acid transfer to the surface, and rate of fluid loss from the fracture or wormhole. (Each of these processes is shown schematically in Fig. 1.) processes is shown schematically in Fig. 1.) Reaction kinetics are independent of the geometry in which reaction occurs; therefore, once kinetics have been determined for a given acid-rock system field treatments can be simulated by prediction of the rate of acid transfer to the surface and fluid loss to the formation. Unfortunately, experiments reported to dare do not allow determination of a kinetic model. SPEJ P. 406

A New Method for Measuring Acid Effective Consumption Time in Acid Fracturing

2014 ◽  
Vol 1004-1005 ◽  
pp. 639-647 ◽  
Author(s):  
Jian Ye Mou ◽  
Ke Xiang Zheng ◽  
Hua Jian Chen ◽  
Han Zhang
Keyword(s):  
Reaction Model ◽  
New Method ◽  
Experimental Result ◽  
Acid Rock ◽  
Acid Fracturing ◽  
In Situ Conditions ◽  
Acid Consumption ◽  
Key Factor ◽  
Flow Reaction

In acid fracturing, the fast acid-rock reaction limits live acid penetration distance. Many kinds of acids were developed to reduce the acid-rock reaction rate. Acid effective consumption time in the fracure is a key factor for accurate prediction of live acid penetraiton distance in acid fracturing designs. In this paper, we developed a new method for measuring acid effective consumption time in the fracture and did experimental result matching to obtain effective acid diffusion coefficient with a acid flow-reaction model. Firstly, we designed a apparatus and corresponding experimental procedure. Then used the new method to measure the effective consumption time for gel acid and crosslinked acid. The new method uses reservoir core samples and is convenient to heat all the fluid as well as pipe lines to the reservoir tempeature, which reflects in-situ conditions more reliably. In the experiment, the rock mass loss with time was measured, based on which the acid consumption time is predicted. Under the experiment conditoins, the gel acid has a effecive consumption time about 17-minute, and the crosslinked acid has about 22-minutes at 130°. Finally, a model of acid flow-reaction in a fracture was used to match experimental results to obtained the acid diffution coeffecient. The results from this study help improve accuracy in acid fracturing designs.

Acidizing Workflow for Optimized Well Performance in Zhdanov and Lam Oil Fields Offshore Caspian Sea

2021 ◽  
Author(s):  
Ruslan Kalabayev ◽  
Ekaterina Sukhova ◽  
Gadam Rovshenov ◽  
Roman Kontarev
Keyword(s):  
Experimental Data ◽  
Caspian Sea ◽  
Laboratory Testing ◽  
Efficiency Calibration ◽  
Oil Fields ◽  
Reservoir Rock ◽  
Rock Matrix ◽  
Acid Rock ◽  
Matrix Acidizing ◽  
Acid Treatments

Abstract Successful sandstone matrix stimulation treatments require addressing complex mineralogy, correctly identifying formation damage, selecting the best stimulation fluids, and placing these fluids correctly. The objective of this paper is to demonstrate a workflow considering laboratory testing, advanced software modeling including acid and diverter fluid efficiency calibration using field experimental data, field execution, and relevant case studies in two oil fields located in the Cheleken block, offshore Caspian Sea. Implementation of the workflow has led to positive results. Matrix acidizing was selected as the primary method for restoring production of the oil wells drilled into sandstone reservoirs due to the reservoir characteristics. Deep Zhdanov wells and shallower Lam wells possess ~15 and ~250 md permeability and ~90 and ~50°C static reservoir temperature, respectively. The target rock mineralogy in both fields predominantly consists of quartz, chlorite, and carbonate minerals. Fluids selection, stimulation design and job execution followed the above mentioned workflow. Treatment modeling considered calibration factors derived from field testing and incorporated several acid and diverter systems. A mix of bullhead and coiled tubing placed treatments were employed. The first step of the workflow considered characterization of the rock mineralogy and selection of the best-fit treatment fluids. Rock dissolution and X-ray diffraction (XRD) tests were run to develop the optimum formulations for the treatment conditions. Further, the results of the laboratory testing were incorporated into the advanced matrix acidizing simulator to model and optimize the treatment schedules. The recently developed matrix stimulation software incorporates geochemical, thermal, and placement simulations calibrated with experimental data. Offset well stimulation treatment pressure match was done by calibrating the acid and diverter fluid efficiency, and those calibrated values were considered for design simulations for the following acid treatments. In this paper, the term "acid efficiency" is defined as a measure of the relative rate at which the acid can penetrate when it flows in the rock matrix as a function of matrix porosity and the overall acid reactivity. The term "diverter efficiency" is defined as a measure of the viscosity developed by a given diverter when it flows in the rock matrix. Such a calibration method accounts for the actual reservoir large-scale acid-rock reaction kinetics. Finally, diagnostic tests and main acid treatments were executed that enabled achieving the desired levels of skin reduction, reservoir placement, zone coverage, and hydrocarbon production rates. Several acid stimulation operations were conducted including three cases in which a low-temperature well with carbonate damage needed repeated acidizing and two additional cases that involved wells with deep, hot, and clay-rich pay zones. Several fluid schedules were applied including foam diversion technique. The above approach uses a unique method of acid efficiency calibration using field experimental data. It requires good knowledge of reservoir rock mineralogy, porosity, and permeability profiles in the zones of interest. Pretreatment skin is calibrated using production data prior to acid efficiency calibration based on matching the actual treatment pressures. The pressure behavior observed during the following treatments closely matched the design pressures confirming applicability of the approach.

Analyzing the Dynamics of Mineral Dissolution during Acid Fracturing by Pore-Scale Modeling of Acid-Rock Interaction

SPE Journal ◽  
2021 ◽  
pp. 1-14
Author(s):  
Jiahui You ◽  
Kyung Jae Lee
Keyword(s):  
Numerical Model ◽  
Multiphase Flow ◽  
Scale Model ◽  
Pore Scale ◽  
Acid Rock ◽  
Rock Interaction ◽  
Acid Fracturing ◽  
Geometry Model ◽  
The Impact ◽  
Pore Scale Model

Summary Hydrochloric acid (HCl) is commonly used in acid fracturing. Given that the interaction between acid and rock affects multiphase flow behaviors, it is important to thoroughly understand the relevant phenomena. The Darcy-Brinkman-Stokes (DBS) method is most effective in describing the matrix-fracture system among the proposed models. This study aims to analyze the impact of acid-rock interaction on multiphase flow behavior by developing a pore-scale numerical model applying the DBS method. The new pore-scale model is developed based on OpenFOAM, an open-source platform for the prototyping of diverse flow mechanisms. The developed simulation model describes the fully coupled mass balance equation and the chemical reaction of carbonate acidizing in an advection-diffusion regime. The volume of fluid (VOF) method is used to track the liquid- and gas-phase interface on fixed Eulerian grids. Here, the penalization method is applied to describe the wettability condition on immersed boundaries. The equations of saturation, concentration, and diffusion are solved successively, and the momentum equation is solved by pressure implicit with splitting of operators method. The simulation results of the developed numerical model have been validated with experimental results. Various injection velocities and the second Damkohler numbers have been examined to investigate their impacts on the CO2 bubble generation, evolving porosity, and rock surface area. We categorized the evolving carbon dioxide (CO2) distribution into three patterns in terms of the Damkohler number and the Péclet number. We also simulated a geometry model with multiple grains and a Darcy-scale model using the input parameters found from the pore-scale simulations. The newly developed pore-scale model provides the fundamental knowledge of physical and chemical phenomena of acid-rock interaction and their impact on acid transport. The modeling results describing mineral acidization will help us implement a practical fracturing project.

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