TX 75083-3836, U.S.A., fax 01-972-952-9435. Abstract:An appropriate post-stimulation clean-up process for matrix acidizing treatments in carbonate reservoirs is essential to ensure that the created wormholes are not damaged by precipitation of the reacted fluids. This paper presents a methodology to compare the performance of the clean-up injection displacement technique with that of the flowback technique. These two techniques were attempted in several seawater injectors in a Saudi Arabian oil field. Several variables that control the flow performance are normalized to accurately evaluate and compare the two post-stimulation clean-up techniques.Based on a well defined criterion, the study analysed historical data from 72 treatments: 42 treatments employing the post-stimulation flowback technique and 30 treatments employing the injection displacement technique. A detailed statistical analysis using actual data from these wells was also carried out.The results indicate that the flowback technique outperforms the injection displacement technique. 2. Thomas, O.A. and Alan, P.R.
During the last 5 years, one of the most common matrix acidizing enhancement techniques used to improve zonal coverage in open hole or cased hole wells is conducting a distributed temperature survey (DTS) using coiled tubing (CT) equipped with fiber-optic and real-time downhole sensors during the preflush stage before the main stimulation treatment. This is used to identify high and low intake zones so the pumping schedule can be modified to selectively place diverters and acidizing fluids with a high degree of control. Once stimulation treatment has been completed, a final DTS analysis is performed to evaluate the zonal coverage and effectiveness of the diversion. Even though this technique has provided satisfactory results, alternative methods providing faster and more accurate understanding of flow distribution between the zones and laterals are needed, especially if there is limited temperature contrast between fluids and reservoir. Thus, an innovative coiled tubing real-time flow tool has been recently developed to monitor flow direction and fluid velocity. This measurement is based on direct measurement of the heat transfer from the sensors to the surrounding fluid using a calorimetric anemometry principle. The first worldwide use of this technology in a Saudi Aramco injector well showed this to be a viable new approach to downhole flow monitoring that can be used by itself or in conjunction with DTS, depending on the constraints of each individual intervention.
Drilling wells with longer horizontal sections to maximize the reservoir contact has brought many challenges to the well interventions using Coiled Tubing (CT). In most cases, the complexity has pushed the CT interventions to the limits, driving the development of new solutions to extend the reach to the total well depth. The number of these extended wells has grown significantly in recent years in Saudi Arabia, especially in new development fields like the study area, where more than 100 extended reach power water injection wells were placed in the reservoir flanks. The water injection wells in this study area are a typical example of complexity due to the combination of large bore tubular, lower reservoir pressure, and long horizontal openhole completion, with lengths between 4,000 to almost 8,000 ft. During the initial CT interventions in this field, several challenges were encountered, e.g., stuck CT due to pressure differentials and slack-off weight through severe doglegs, tight spots, and other obstructions. Extensive knowledge was gained by performing an extensive simulation and study of the horizontal section geometry, and analyzing the operational data. Based on the findings, a combination of techniques was introduced to the CT intervention procedure, to extend the reach and minimize the operational problems and costs. The key components of our new implemented methodology were buoyancy reduction by using nitrified fluids and friction reduction by using new viscoelastic surfactant (VES) friction reducer. In addition, combinations of other techniques were employed, e.g., optimizing the pull tests frequency in openhole and improving CT movement practices. This paper shows the effectiveness of the new cost effective and reliable methodology to maximize the CT reach up to 8,000 ft allowing the distribution of the acid stimulation throughout the entire horizontal sections. INTRODUCTION This paper is based on the CT stimulation campaign performed in one of the new fields in Saudi Arabia that is being developed by drilling extended reach horizontal water Injection wells (Figure 1) in the flank of the reservoir to assure the effective water distribution, optimum sweeping and pressure support in the reservoir. Acid stimulation using CT is not an easy process due to the wellbore architecture, length of the horizontal section, reservoir hetrogentiy, low reservoir pressure, damage distribution, etc. For carbonate formation, the success of HCl acid stimulation depends on the placement and effective acid distribution along the entire openhole. Although CT represents the most effective placement method in a horizontal section, it has some limitation especially on extended reach wells with complex configuration. The definition of an extended reach well is a well with a measured depth to true vertical depth ratio (MD/TVD) equal to or greater than 2.
Drilling new generation wells with longer horizontal sections, to maximize the reservoir contact, has brought many challenges to well interventions using Coiled Tubing (CT). In most cases, the complexity has pushed CT interventions to the limits, driving the development of new solutions to extend the reach to total well depth. The number of these extended-reach wells has grown significantly in recent years in Saudi Arabia, especially in this new development field where more than 120 extended reach water injection wells were placed in the reservoir flanks. The water injection wells in this study area are complex due to the combination of large bore tubular, lower reservoir pressure and horizontal openhole (OH) completion, with lengths from 3,000 ft to almost 5,000 ft. During the initial CT interventions in this field, several challenges were encountered, e.g., stuck CT differentials, slack-off weight through severe doglegs, tight spots, and other obstructions. Extensive knowledge was gained by performing an extensive simulation, studying the horizontal section geometry and analyzing the operational data. Based on the findings, combinations of techniques were introduced to the procedure to extend the reach and minimize the operational problems and costs. The key components of our new implemented strategy were buoyancy reduction by using nitrified fluids and new viscoelastic surfactant (VES) friction reducer or drag reduction agents. In addition, combinations of other techniques were employed, e.g., optimizing the pull tests frequency in the OH and improving CT movement practices. This paper discusses the difficulties and challenges of the initial stage of the stimulation campaign, performed in horizontal OH water injector wells using CT. Also, it presents the results and analysis of the effect of buoyancy, CT pipe size and new friction reducer for the referenced wells. The study leads to a new cost effective and reliable technique, which once implemented, conduces to maximize the CT reach without using mechanical devices, e.g., agitators or tractors. INTRODUCTION The study was performed in one of the new fields being developed in Saudi Arabia by drilling extended-reach horizontal water injection wells in the flank of the reservoir to help assure the effective water distribution, optimum sweep and adequate pressure support in the reservoir. Stimulation of the new water injection wells is a key factor for new increment success. The horizontal wells were acid stimulated, in order to remove formation damage and enhance the water injection. Distribution of treatment on the whole horizontal section is essential to implement the depletion strategy and maximize recovery factor. The length of horizontal OH section varies between 3,000 ft and 5,000 ft.
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