Zadco Experience In Stimulating Multi-Lateral Wells Offshore Abu Dhabi
Abstract: This paper was prepared for presentation at the 1998 Abu Dhabi International Petroleum Exhibition and Conference held in Abu Dhabi, 11-14 October 1998.
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There are several types of drilling methods to increase the productivity of a well, such as horizontal drilling, extended reach horizontal drilling and Multilateral (ML) drilling. It is thought that ML wells could be more economic with higher productivities than horizontal or extended reach horizontal wells. Advances in ML drilling promise reduced costs, greater flexibility and increased profit potential. In the last 20 years, thousands of ML wells have been drilled worldwide, but only a small percentage of the total number of wells is multilateral. The probable reason may be lack of concise information and misconceptions surrounding the costs and perceived risks. However, recent advances in the capabilities of the systems and applications have proved ML drilling to be a truly revolutionary and cost effective solution for the industry. This paper investigates the benefits of ML drilling as one of the highly expanded methods. Moreover, advantages, challenges, and priorities of the ML technology are highlighted. Since application of ML wells requires some improvement and development especially in the Middle East, therefore, two case studies from this region are presented. The first case study is the first Saudi Aramco's deep ML gas well, and the second is drilling a dual lateral well in Dukhan field in Qatar. For the first case study, productivity of ML wells is presented. Furthermore, a comparison is made between the productivity of a horizontal and dual ML in order to give a recommendation for one of them. Introduction Unconventional drilling technologies play a key role today where conventional technologies are not fully efficient to keep development profitable. These technologies allow us to increase production per well but also to improve ultimate reservoir recovery factor (RF). Multilateral (ML) drilling is one of unconventional drilling technologies emerging at the beginning of nineties.1 More than 10 percent of the total 74000 drilled wells in the world is ML. The general definition of a ML well is one in which there is more than one horizontal or near horizontal lateral well drilled from a single side (mother bore) and connected back to a single bore. 2 MLs can be divided into two categories:Re-entries: in this category an existing well is re-entered and new branches are drilled off the existing wellbore (e.g. Charlez and Breant 1999 1, Tantawi et al. 1998 3).New developments: in this category a new well is drilled as a ML well.
There are several types of drilling methods to increase the productivity of a well, such as horizontal drilling, extended reach horizontal drilling and Multilateral (ML) drilling. It is thought that ML wells could be more economic with higher productivities than horizontal or extended reach horizontal wells. Advances in ML drilling promise reduced costs, greater flexibility and increased profit potential. In the last 20 years, thousands of ML wells have been drilled worldwide, but only a small percentage of the total number of wells is multilateral. The probable reason may be lack of concise information and misconceptions surrounding the costs and perceived risks. However, recent advances in the capabilities of the systems and applications have proved ML drilling to be a truly revolutionary and cost effective solution for the industry. This paper investigates the benefits of ML drilling as one of the highly expanded methods. Moreover, advantages, challenges, and priorities of the ML technology are highlighted. Since application of ML wells requires some improvement and development especially in the Middle East, therefore, two case studies from this region are presented. The first case study is the first Saudi Aramco's deep ML gas well, and the second is drilling a dual lateral well in Dukhan field in Qatar. For the first case study, productivity of ML wells is presented. Furthermore, a comparison is made between the productivity of a horizontal and dual ML in order to give a recommendation for one of them. Introduction Unconventional drilling technologies play a key role today where conventional technologies are not fully efficient to keep development profitable. These technologies allow us to increase production per well but also to improve ultimate reservoir recovery factor (RF). Multilateral (ML) drilling is one of unconventional drilling technologies emerging at the beginning of nineties.1 More than 10 percent of the total 74000 drilled wells in the world is ML. The general definition of a ML well is one in which there is more than one horizontal or near horizontal lateral well drilled from a single side (mother bore) and connected back to a single bore. 2 MLs can be divided into two categories:Re-entries: in this category an existing well is re-entered and new branches are drilled off the existing wellbore (e.g. Charlez and Breant 1999 1, Tantawi et al. 1998 3).New developments: in this category a new well is drilled as a ML well.
Multilateral drilling (ML) drilling technology is one of the unconventional drilling methods to increase the productivity of a well. It is thought that ML wells could be more economic with higher productivities than other types of wells such as vertical, directional, horizontal or extended reach horizontal wells. Advances in ML drilling has resulted in significant cost saving, greater flexibility and increased profit potential. In the last two decades, thousands of ML wells have been drilled worldwide. Around 10 percent of the total wells are ML. During 1980s, advances in horizontal technology were adopted quickly in the Middle East to bring about dramatic improvements in well productivity. Many operators in the Persian Gulf region looked at ML drilling technology as a next step from horizontal drilling technology. These operators started to drill ML wells after experiencing successful drilling of horizontal wells. Since the early 1990, the use of ML drilling technology in the Middle East has seen significant growth to the extent that Middle East is one of the most active areas in the world for ML applications. This paper investigates the benefits of ML drilling as one of the highly expanded methods. Advantages and challenges of the ML technology are highlighted. Since Middle East is one of the most active areas in the world for ML applications, therefore, two case studies from this region are reviewed. The first case study is the first Saudi Aramco's deep ML gas well, and the second is drilling a dual lateral well in Dukhan field in Qatar. For the former case study, productivity of ML wells is presented. Furthermore, a comparison is made between the productivity of a horizontal and dual ML in order to give a recommendation for one of them. Introduction Unconventional drilling is a growing part of the global drilling activity. In the past several years directional, horizontal, extended reach horizontal and multilateral (ML) wells have been drilled successfully using unconventional drilling techniques. Unconventional drilling technologies play a key role today where conventional technologies are not fully efficient to keep development profitable. These technologies allow us to increase production per well but also to improve ultimate reservoir recovery factor (RF). ML drilling as one of unconventional drilling techniques emerged at the beginning of nineties.1 The general definition of a ML well is one in which there is more than one horizontal or near horizontal lateral well drilled from a single side (mother bore) and connected back to a single bore. 2 During 1980s, advances in horizontal technology were adopted quickly in the Middle East to bring about dramatic improvements in well productivity. Many operators in the Persian Gulf region looked at ML drilling technology as a next step from horizontal drilling technology. These operators started to drill ML wells after experiencing successful drilling of horizontal wells. Since 1992, the use of ML drilling technology in the Middle East has seen significant growth to the extent that Middle East is one of the most active areas in the world for ML applications. 3 In 1996, it is estimated that over 35 MLs were drilled in the Middle East. 4 Among the Middle East countries, some invested more on of ML technology are Saudi Arabia, UAE, Oman, and Qatar. Examples of leading companies in the region in ML technology are Saudi Aramco and ZADCO. Other countries in the region are progressing in application of ML technology. An overview to applicability of ML technology in the Middle East countries has been done by Mirzaei Paiaman and Moghadasi (2009).5
Filter-Cake Cleanup in MRC Wells Using Enzyme/Surfactant Solutions
Long horizontal and multi-lateral wells continue to be used in applications requiring high production rate. However, many of these wells suffer from low productivity due to incomplete filter cake removal. The obstacles encountered are the difficulty to ensure contact of the cleaning fluids with the filter cake throughout the whole interval, as well as controlling the reaction rate between the cleanup fluids and the filter cake to assure uniform dissolution. The filter cake formed by water-based mud consists of XC-polymer, starch, CaCO3 particles and drilling cuttings. Today several chemical techniques (oxidizers, enzymes and acids) are available to break the polymers and dissolve CaCO3 particles that are present in the filter cake. The limitations of these fluids are fast reaction rates and corrosiveness provided by acids, especially at high temperatures. Also, cleaning fluids are not effective in heterogeneous formations where there are high permeability streaks, which will require using large volumes of the treatment fluids, but with poor performance. One way to overcome problems associated with the heterogeneous nature of oil and gas reservoirs is to increase the viscosity of the cleaning fluids. This was addressed in the present study by adding a viscoelastic surfactant to the cleaning fluids (mainly enzymes). Laboratory studies were conducted to examine the effect of viscoelastic surfactants on the performance of specific enzymes (used to break XC-polymer and starch). The apparent viscosity of the combined solution was measured as a function of shear rate (10 to 1,000 s-1) and temperature (77 to 212°F). A modified HPHT fluid loss cell was used to assess the effectiveness of the combined system in cleaning filter cake formed by water-based drilling mud. The effects of temperature, enzyme type and concentration; and surfactant concentration were investigated. Experimental results showed that the surfactant increased the viscosity of the solution. As a result, the rate of polymer degradation by enzymes had decreased. Solutions that contain enzymes and viscoelastic surfactants can give a uniform distribution over the whole interval, which will result in higher production rates. This paper will discuss various interactions of surfactant-enzyme systems and address the advantages and limitations of this system. Introduction The use of horizontally drilled wells has increased dramatically during the past decade because they offer greater contact with the reservoir rocks. The effective production rate should be much greater for horizontal well. Unfortunately, the larger drainage area and longer wellbore also contribute to a larger exposed area and longer exposure time for the drilling fluid in horizontal wells. Therefore, severe damage caused by drilling fluid can have a considerable influence on the reduction of horizontal well productivity.[1] Near-wellbore formation damage can result from many activities during drilling, completion, and production. One of the most pervasive damage mechanisms is pore plugging by solid particles from drilling mud, drilled solids, or particles from the formation.[2] It is not always possible to prevent formation damage, and well stimulation techniques have been used to remove or mitigate the effect of formation damage for more than half a century. Although conventional well-stimulation techniques have been used very successfully, they have significant limitations in long horizontal wells and in wells with multiple branches.[3] More and more new wells have a tendency to be complex, with slotted liners or screen completions, maximum reservoir contact (MRC),[4] multiple horizontal sections and, in some cases, sensitive downhole instrumentation. Saudi Aramco's definition of MRC wells requires that the horizontal interval must contact at least 4,000 ft of the targeted reservoir(s).[5] Such wells would benefit from a stimulation method that eliminates the need for aggressive chemicals and the difficulties associated with fluid placement. Drill-in fluids are generally water-based muds (WBMs) containing a viscosifier, a fluid-loss reducer, salts, and sized calcium carbonate particles. For temperatures less than 260°F, conventional polymers are used for viscosity and fluid loss control. Solid particles are added for pore throat bridging, where the particle size distribution (PSD) of the CaCO3 is defined and matched for the permeability range of the formation being drilled.
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