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The continuous and increasing demand for oil and gas coupled with already recognized Brown Field stage of many of the major producing reservoirs led the operating companies to re-focus their attention on quick incremental production gains to supplement the drilling activity. These conditions promoted the interest for well intervention and stimulation in Brunei. The arrival of a multipurpose rig capable of handling the operating environment facilitated this intervention in the shallow water offshore of Brunei. This paper demonstrates the impact on the so called Brown Field of shifting the focus from field development to incremental production recovery. It will address the importance of vessel and well candidate selection processes, fluid selection and in particular, the well flow back as a critical stage to maximize well performance. Case histories are used to formulate and offer technical process recommendations for well intervention activities with consolidated experience of project undertaken by Brunei Shell Petroleum (BSP) during the Coil Tubing Stimulation campaign of 2004/05, assisted by the multipurpose service vessel BIMA. It discusses the challenges encountered, the advantages of selected operating vessel and its impact on delivering the expected results. Background Brunei Shell Petroleum (BSP) is a company partnered by the Government of Brunei and Shell International and has surpassed 75 years of drilling life and is well into the billion barrel mark of produced oil from over 2000 wells drilled. As most of the wells are maturing, a stimulation campaign is planned to meet the company production targets. Generally the petroleum industry has relatively low focus on production recovery through well intervention and matrix stimulation, compared to drilling new wells. The uncertainty and risk are perceived to be too high to justify the investment on stimulation business in comparison with drilling. An intervention campaign typically requires a detailed study of shut-in, and under performing wells to identify the right candidates for stimulation.1 Potential gaps in well data may increase the uncertainty, and make the choice of the right technique and fluids for achieving the "set out" objective for the production recovery of the well more difficult. The first step and perhaps the most critical one during well intervention is the right candidate selection. This initial process of identifying the right well is very critical for a number of reasons, the most obvious being the classification of the well based on production potential. The study and proposal of the optimum treatment technique to match available economics and resources must also be addressed at the candidate selection stage. Gaps in Well data are the biggest obstacle to the initial stage of well intervention. In many cases this is due to the fact that the well ownership is temporarily transferred to the operations teams (drilling, completion or well services). The details in the Well History File are usually on the completion hardware changes and intervention history. It is quite often that the well data details of the reservoir mineralogy, well testing and production (hydrocarbon and water) data are lacking. Data gaps described above are a result of the well construction focus on field development when the lifting costs are less favorable to the operator. Data gaps are not common-place, however, a single event can and in most cases will, result in failure to achieve the "set out" objective. The expertise required for well intervention activities combined with multi-discipline knowledge base is difficult to be found in a single environment. Bringing together and promoting the collaboration between the different discipline champions from operators and contractors are of paramount importance for achieving objectives.
The continuous and increasing demand for oil and gas coupled with already recognized Brown Field stage of many of the major producing reservoirs led the operating companies to re-focus their attention on quick incremental production gains to supplement the drilling activity. These conditions promoted the interest for well intervention and stimulation in Brunei. The arrival of a multipurpose rig capable of handling the operating environment facilitated this intervention in the shallow water offshore of Brunei. This paper demonstrates the impact on the so called Brown Field of shifting the focus from field development to incremental production recovery. It will address the importance of vessel and well candidate selection processes, fluid selection and in particular, the well flow back as a critical stage to maximize well performance. Case histories are used to formulate and offer technical process recommendations for well intervention activities with consolidated experience of project undertaken by Brunei Shell Petroleum (BSP) during the Coil Tubing Stimulation campaign of 2004/05, assisted by the multipurpose service vessel BIMA. It discusses the challenges encountered, the advantages of selected operating vessel and its impact on delivering the expected results. Background Brunei Shell Petroleum (BSP) is a company partnered by the Government of Brunei and Shell International and has surpassed 75 years of drilling life and is well into the billion barrel mark of produced oil from over 2000 wells drilled. As most of the wells are maturing, a stimulation campaign is planned to meet the company production targets. Generally the petroleum industry has relatively low focus on production recovery through well intervention and matrix stimulation, compared to drilling new wells. The uncertainty and risk are perceived to be too high to justify the investment on stimulation business in comparison with drilling. An intervention campaign typically requires a detailed study of shut-in, and under performing wells to identify the right candidates for stimulation.1 Potential gaps in well data may increase the uncertainty, and make the choice of the right technique and fluids for achieving the "set out" objective for the production recovery of the well more difficult. The first step and perhaps the most critical one during well intervention is the right candidate selection. This initial process of identifying the right well is very critical for a number of reasons, the most obvious being the classification of the well based on production potential. The study and proposal of the optimum treatment technique to match available economics and resources must also be addressed at the candidate selection stage. Gaps in Well data are the biggest obstacle to the initial stage of well intervention. In many cases this is due to the fact that the well ownership is temporarily transferred to the operations teams (drilling, completion or well services). The details in the Well History File are usually on the completion hardware changes and intervention history. It is quite often that the well data details of the reservoir mineralogy, well testing and production (hydrocarbon and water) data are lacking. Data gaps described above are a result of the well construction focus on field development when the lifting costs are less favorable to the operator. Data gaps are not common-place, however, a single event can and in most cases will, result in failure to achieve the "set out" objective. The expertise required for well intervention activities combined with multi-discipline knowledge base is difficult to be found in a single environment. Bringing together and promoting the collaboration between the different discipline champions from operators and contractors are of paramount importance for achieving objectives.
Improving oil and gas production from the Brown Fields is now more important than ever to the operating companies, as the oil price remains record high. Matrix stimulation is often preferred as it could generate additional production gain with relatively low level of investment. In the recent acidizing campaign in Brunei, a particular challenge was the flowback of tubing pickling and spent acids, and neutralization of the spent acid on the surface. A series of effective methodologies for the stimulation of offshore multilayer sandstone oil reservoirs was implemented. The chemistry and art of four different acidizing methods involving Tubing Pickling, Bullheading, Diversion and Coiled Tubing placement were used. Stimulation of over forty wells utilizing different acid systems and procedures resulted in noticeably different production gains. The short and long term results are correlated with the stimulation procedures and practices. The present paper describes a comparison of procedures and production gains during these acid stimulation treatments. The cost, logistics and operational constraints due to specific Brunei offshore environment and conditions will also be discussed. Post-treatment production gain is correlated with the efficiency and timing of the flowback process. Use of computer-based virtual laboratory tool for the fluid selection, coreflow laboratory testing for the fluid optimization at downhole conditions and evaluation of fine migration tendencies were investigated before the treatment. The results were compared with the one from other operators in the same environment and reservoir conditions. Review of post acidizing results came up with recommendations and lesson learnt for future campaigns. This effort will certainly enhance the success ratio of the sandstone acidizing treatments. Significance: Developed lessons learnt to increase the success ratio of sandstone stimulations. Introduction Sandstone acidizing is possibility the most complicated stimulation method as it involves complex chemical reactions in the near wellbore matrix1,2,3,4,10,16. Unlike carbonate acidizing where the simulation fluids are used to dissolve the rock around the damage materials, sandstone acidizing aims at dissolving and dispersing the minerals and damage materials in the pores of the reservoir formation. For this reason, the stimulation results using the known standard acid fluid formulations for different reservoir formations and for different wells in the same reservoir can vary widely. Optimization of the sandstone acid stimulation fluids may now be done by numerical simulation of chemical reactions.17 However, it will need a large amount of data not only on detailed mineral compositions of the targeted simulation zones but also on nature, location and extent of the damage materials in the near wellbore matrix. In addition, reaction products due to the reactions of the stimulation fluids with various mills and scales in the tubular and in the pumping equipment can also upset the optimized acid formulation; cause adverse reactions with the formation minerals; and further aggravate the overall complex chemistry involved in the sandstone stimulation process.5 Accordingly, the need to have a proper tubing pickling procedure with proper pickling acid fluid had been repeatedly emphasized. Recent marked effort in this regard included an analytical modeling of the tubing pickling process and its verification using field acidizing job data6,7. The studies showed that the process again involved the three basic mechanisms namely surface reaction, diffusion, and convection, and the art of balancing these three fundamental forces encountered in all sandstone and carbonate stimulation. Generic Sandstone Acidizing Procedure Summarizing the known arts of sandstone acidizing, the following can be served as a recommendation for a generic but minimum standard sandstone acidizing fluid pumping procedure:
Generally, matrix acidizing fluids for sandstone are executed in the field only after core tests qualify their ability to remove damage. However, most cores that are used come from sandstone quarries and the cores are largely clean and undamaged (and not representative of the sandstone conditions in actual producing wells). This study proposes novel applications of straightforward chemistry to synthesize calcium carbonate particles that damage the porosity of clean sandstone cores (in core flow tests); the study includes reactions carried out under controlled conditions as well as within the pore space of sandstone cores. In the controlled reactions, solutions of calcium chloride are mixed with solutions containing one of a variety of soluble inorganic or organic carbonates, and the reaction generates calcium carbonate particles. The resulting particles were characterized using both light scattering and scanning electron microscopy (SEM). The reaction rate and size distribution of calcium carbonate particles varies depending on the temperature, stir rate, chemistry of the carbonate species, and the concentrations (and concentration ratio) of calcium brine and carbonate species. This technique is also applied in actual core tests, where a sandstone core saturated in calcium brine is exposed to a solution of the soluble carbonate species and generates calcium carbonate solid (damage) throughout the length of the core from the injection face. The final permeabilities of cores subjected to this treatment exhibit damage compared to before the treatment, which is likely due to the precipitation of calcium carbonate solids. This method for damage generation has ramifications in the screening of a variety of stimulation fluids, including acids and scale inhibitors.
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