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Вестник Пермского национального исследовательского политехнического университета. Геология. Нефтегазовое и горное дело
Changes in the properties of fluids and chemical reactions products caused by acid treatment of carbonate reservoirs2019 •
2012 •
Successful mechanical cleanouts and acid stimulations in production and injection wells at the Berlin, Ahuachapan, Chinameca and San Vicente geothermal fields were performed over the past 12 years, providing great improvements in power generation and permeability enhancement in injection wells. The application of these techniques delivered an accumulative increase of more than 70 MWe in power production and 900 kg/s of injection capacity. Chemical stimulations, using a drill rig to clean up to four zones, have given improvements close to 200%, while acid jobs through the well head have given 40%, when cleaning only the first permeable zone. It has been applied to production wells with mud and cutting damage, production wells with calcite scaling and injection wells with silica scale and mud damage or positive skin values, and has also been successfully applied in injection wells with negative skin. The fluid treatment mostly used in Berlin production wells is the Mud Acid 10:5, RPHF...
Proceedings of SPE Annual Technical Conference and Exhibition
A Novel Technique to Acidize Horizontal Wells with Extended Reach2004 •
Substantial production/ injection improvements can be achieved with matrix stimulation if treatments are engineered properly. The systematic approach to stimulation treatments consists of candidate selection, formation damage characterization, stimulation technique determination. Candidate selection for matrix stimulation is based on finding wells with impaired productivity and diagnosing the cause of the impairment. There are several reservoirs with varied mineralogical and petro-physical properties. The heterogeneity of these reservoirs poses a challenge towards an effective matrix stimulation job design and execution. To achieve the desired results, the job design for each well needs to incorporate not only studies of the reservoir properties but also close monitoring and analysis of the matrix stimulation jobs previously carried out in the same reservoir. It has been observed that the recommended formulation based on only laboratory studies does not always yield the desired results. Lots of formulations based on recommended studies with subtle variations have been tried and the results have been found to be of mixed nature. In some wells, the results are excellent and in some cases it is not satisfactory. This mixed result has come up as a challenge to the stimulation engineers involved in design and execution of matrix acid jobs. Well Stimulation Services, Ahmedabad executes around 300 matrix acid stimulation jobs per year and the meticulous evaluation of these acidization jobs makes stimulation a learning process, leading towards improved design and better results. This paper deals with the improvement in matrix acidization job design and execution achieved at western onshore fields of India by changes made after analysis of compiled laboratory studies, review of all executed acid job parameters and the formulations used, brainstorming and discussion. Each and every field of Western onshore has been analyzed in detail and a formulation most suitable for each field and each type of well has been developed.
SPE Production Engineering
An Analysis of Reservoir Chemical Treatments1988 •
Summary. In chemical well treatments, success or failure is often difficult or impossible to anticipate. The near-wellbore pressure drawdown and fines migration contribute to the overall well damage, but the effect of the chemical treatment alone can induce damage by reprecipitation when the spent treatment solution is produced over the treated zone. The identity, amount, and rate of return of this repre-cipitation damage are discussed here.ur procedure considers the chemical interaction of formation minerals and brine with the treatment solution in the presence of an immiscible phase. Although this analysis contains several simplifying assumptions, the results can be applied, with care, to lend insight and direction to practical problems. If relative permeabilities and mineral and injected water compositions are known, the permeabilities and mineral and injected water compositions are known, the analysis procedure will estimate the success of the treatment and indicate approximate ...
International Journal of Engineering Research and Technology (IJERT)
IJERT-Coiled Tubing Acidizing: An Innovative Well Intervention for Production Optimization2015 •
https://www.ijert.org/coiled-tubing-acidizing-an-innovative-well-intervention-for-production-optimization https://www.ijert.org/research/coiled-tubing-acidizing-an-innovative-well-intervention-for-production-optimization-IJERTV4IS060548.pdf In the Oilfield Services, Coiled Tubing (CT) is considered as one of the most adaptable and flexible technology. Since its introduction, some forty years ago, Coiled Tubing has aggressively evolved in oil and gas industry. Liquid unloading of the wells and sand clean out were the early applications of the Coiled Tubing. Now-a-days, CT is very frequently used in different well interventions, perforating the well and above all the recent developments of the Coiled Tubing Drilling. A lot of other services employed in the past but they showed decline, while CT has shown a growing rate of 10% per year. The speed and convenience of Coiled Tubing has been used to provide benefit to well productivity in different applications. Some common applications of CT are the fracturing, well testing, unloading of the well, acidizing, scale milling and other intervention activities. Today, engineers can change the toughest well into a profitable production well by using the speed and convenience of the CT, strong engineering planning, creative integration and other complementary equipment. In this paper only one application of CT is considered i.e. acidizing. The main purpose of this project was to increase the deliverability of a gas reservoir in which gas production has been reduced due to near well bore damage (skin). The case study is performed for such a well in which production is impaired by skin & reservoir rock is carbonate. The skin value is determined through well testing. The production data before acidizing & well testing has confirmed a high value of skin. Inflow performance relationship at current value of skin is plotted. This plot shows that the production is not up to the mark. To make it economical as well as favorable, stimulation has been performed to reduce the skin. By reducing the skin a considerable increase in production is observed. The entire work has been done on MS Excel. This technique results enhanced productivity of well accelerating hydrocarbons recovery & adding them to the reserves.
2015 •
As a result of the rapid reduction in productivity of well B14, south west of the Niger Delta region, the need to investigate the cause of the damage was initiated. When it was identified fine migration as the major cause of the production decline, acid stimulation was recommended as the mitigation strategy. Acid (matrix) stimulation practice involves the pumping of acid into the formation through the wellbore at the rates and pressures below the fracture gradient of the formation. Conventionally, hydrochloric acid (HCL) is used for carbonate formations while hydrofluoric acid (HF)/ mud acid (HCL +HF) is best suited for sandstone formations. Also, in a very high damaged formation and very high temperature environment that requires prolong contact of the HCL acid with the steel pipe, due to the severe corrosion that will occur, organic acids are more suitable. In stimulating this well, mud acid was used and the well was stimulated using organic mud acid or organic clay acid. Stimulat...
All wells are susceptible to formation damage to some degree, ranging from relatively minor loss of productivity to plugging of specific zones. Formation damage could simply be referred to as a term used to emphasize reduced current production. Acidizing is a well stimulate technique where acids are primarily used to remove or cure damage around wellbore caused by drilling, completion, production and work over operations in order to improve production. In matrix acidizing, acid is used to remove the damage near the wellbore. This removal of severe plugging in sandstone, limestone or dolomite by matrix acidizing process can lead to large increase in well productivity. It is expected that matrix acid treatment should remove flow restrictions near the wellbore and allow the well to produce at an undamaged rate. However, the production rate after treatment is sometimes lower than predicted or in extreme cases without any improvement at all. This study evaluates matrix acidizing operations in oil producing wells with a view to identifying causes of acidizing failures and developed a systematic approach to matrix acidizing that will eliminate failures and greatly enhance the performance of acidized oil wells. Discussions have been centered on the fundamentals of formation damage and acidizing, review of existing literature on the subject and matrix models. In treated wells studied, stimulation ratios from productivity indices were almost equal to or greater than 2 (≥ 2) and always greater than stimulations ratios from production rates, showing that the treatments were positive in reducing or curing damage around the wellbore but the stimulation ratios from the two parameters (productivity index and production rate) were not the same as a result of flow restrictions. Since all treated intervals in the different wells studied showed positive response to damage reduction, it could be concluded that acidizing if properly executed will reduce or cure damage around the wellbore and improve productivity.
Acid injection is the recommended treatment for productivity enhancement in carbonate reservoirs. Acid stimulation is a difficult challenge due to the instability of the dissolution figure, named wormhole, which depends strongly from the nature of the carbonate (heterogeneity). The objective of the study described hereafter is to compare various stimulation strategy to improve current treatment procedures. In matrix acidizing of horizontal wells, the propagation of wormholes as deeply as possible into the formation with the maximum coverage along the wellbore is a major concern. Diverting agents based on polymer crosslinking at high pH are currently used for matrix acidizing (Figure 1). The crosslinking occurs as the acid is consumed. Wormholes formed in the high permeability zone are temporarily sealed and the subsequent acid slug enters the low permeability zone. The treatment is efficient, provided that the diversion procedure is adequately designed. For acid fracturing treatments, the productivity benefit is directly related to the fracture length and conductivity (Figure 2). Maximising the fracture length cannot be achieved without controlling the acid filtration rate from the fracture walls (fluid loss). Since most of the filtration occurs from the wormholes rather than uniformly, it is important to limit the wormhole formation. Finally, the last criteria for the selection of a fracturing fluid is related to the etching of the fracture walls: an irregular etching pattern favours a good fracture conductivity. The experimental methodology described in this paper helps to choose the best strategy in terms of fluid composition, either for matrix acidizing of horizontal wells or for acid fracturing. In the first part, we present the laboratory equipment used to mimic the dynamic process occurring during acid placement and acid fracturing. The discussion of the results gives elements for the implementation of the best strategy for acid treatments in carbonate reservoirs. Experimental design for the simulation of well stimulation. The main originality of the equipment is that it simulates flow from an open-hole or a fracture wall. One or two tangential cells are used for acid fracturing or acid diversion respectively (Figure 3). The fluid is injected continuously in the tangential loop at a high flow rate and enters the core through a ∆P. The volume of fluid recovered at the outlet of the core is measured and the filtration rate is calculated. The acid breakthrough time is recorded and the wormhole propagation rate is calculated. The main parameters are the pressure gradient, the nature of the fluid and the mineralogy of the core, and the temperature. Acid fracturing: behaviour of gelled acids, acids in emulsion and straight acids. Three fluids at an acid concentration of 15%, are compared at 50°C in a 5 md limestone. The filtration rate ranges in the order plain acid > acid in emulsion > gelled acid (Figure 4). The last one has a very low filtration rate and is very powerful to limit fluid loss from the fracture. Acids range in the same order for the wormhole propagation rate. These data are readily explained when considering that the development of wormholes increases the surface area for fluid filtration. In order to appreciate the effect of viscosity, the filtration rate measured with the gelled acid is compared to the filtration rate of water in the same conditions. Indeed, this represents the apparent relative viscosity (η r a) of the gelled acid in porous media (Figure 5). When compared to the relative viscosity of the gelled acid, the value of η r a is very low and ranges from 4 to 10. This shows that there is a considerable loss of viscosity in
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On-Board and Train-to-Wayside Free Space Optical Link: Design and Characterization2020 •
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Effect of sowing dates and nitrogen levels on total dry matter and its partitioning at different growth stages and yield of Indian mustard (Brassica juncea L.)2017 •