Application of New Fracturing Technique Improves Stimulation Success for Openhole Horizontal Completions
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Cited by 11 publications
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As shown by technical papers as early as the 1960s, our industry has long known that hydrajetting perforations or slots through cemented casing could often "bail-out" a problem well that otherwise seemed completely resistant to hydraulic fracturing attempts. For most of the first 50 years of fracturing applications, few operators had sufficient demand for the fracturing process to make it a commodity service, especially before the advent of coiled tubing (CT) services in the 1980s. Often, this type of well service was costly because of the need for both abrasive mixing and high-pressure pumping. In many cases, it was too time consuming to be practical as an "every-well" application, and lower-cost conventional explosive shape-charge perforating seemed sufficient for most wells. As oil and gas prices have drastically increased in recent years, many operators have realized that for some well conditions, the use of hydrajet perforating (HP) can improve fracture stimulation efficiency and well economics. In a few cases HP has proven to be the only way that effective fracture stimulation could be achieved. In the past few years there has been a growing acceptance among both operators and service companies that hydrajet (abrasive jetting) perforating can improve overall well economics for fracture stimulated wells in many reservoirs. Some newer methodologies have combined hydrajet perforating and hydraulic fracturing into a single, continuous, multi-stage stimulation method. For many wells needing multiple fracture stimulations, significant reductions in nonproductive time (NPT) allows for reduced well costs even when more actual fracture stages are pumped. Use of more stages has often provided significant production gains and greater recoverable reserves. Enhanced stimulation success in many moderately hard and very hard formations have proven the value of converting from shape charge perforating to hydrajetting as a stand-alone operation to avoid severe near-wellbore problems during hydraulic fracturing stimulation treatments. Since about 2000, and especially during the most recent 5 years, service providers have progressively expanded the processes, which included hydrajet perforating, especially in conjunction with hydraulic fracturing methods. This paper will review the expanding applications of hydrajet perforating in recent years, including case histories from several global applications. Background Early technical papers tell us that hydrojetting (w/o abrasives) was used with acidizing and fracture acidizing as early as 1939, primarily in zones completed open hole. However, with the incorporation of solid abrasives (hydrajetting, using abrasives) the jetting nozzles in use then could only perform for minutes before excessive erosion became a problem. The literature also reveals that around 1958 there was a renewed interest in sand-jetting and more abrasion-resistant carbide jets were developed. In May, 1961, the Journal of Petroleum Technology included three landmark publications that presented much of what had been happening since 1958 with respect to HP applications, and described other hydrajetting wellbore functions such as jetting cement from casing, cutting casing, scale removal, and other applications. The more extensive of these publications (Brown et al. 1961, and Pittman et al. 1961) had first been presented at technical conferences in October, 1960. The shorter, introductory article (Ousterhout 1961) indicated that by early in 1961 over 5,000 hydrajetting jobs had been performed with a success rate in excess of 90%; more than half of these were perforating applications. At that time, explosive/shape charge perforating was still in its infancy, with bullet perforating still common.
As shown by technical papers as early as the 1960s, our industry has long known that hydrajetting perforations or slots through cemented casing could often "bail-out" a problem well that otherwise seemed completely resistant to hydraulic fracturing attempts. For most of the first 50 years of fracturing applications, few operators had sufficient demand for the fracturing process to make it a commodity service, especially before the advent of coiled tubing (CT) services in the 1980s. Often, this type of well service was costly because of the need for both abrasive mixing and high-pressure pumping. In many cases, it was too time consuming to be practical as an "every-well" application, and lower-cost conventional explosive shape-charge perforating seemed sufficient for most wells. As oil and gas prices have drastically increased in recent years, many operators have realized that for some well conditions, the use of hydrajet perforating (HP) can improve fracture stimulation efficiency and well economics. In a few cases HP has proven to be the only way that effective fracture stimulation could be achieved. In the past few years there has been a growing acceptance among both operators and service companies that hydrajet (abrasive jetting) perforating can improve overall well economics for fracture stimulated wells in many reservoirs. Some newer methodologies have combined hydrajet perforating and hydraulic fracturing into a single, continuous, multi-stage stimulation method. For many wells needing multiple fracture stimulations, significant reductions in nonproductive time (NPT) allows for reduced well costs even when more actual fracture stages are pumped. Use of more stages has often provided significant production gains and greater recoverable reserves. Enhanced stimulation success in many moderately hard and very hard formations have proven the value of converting from shape charge perforating to hydrajetting as a stand-alone operation to avoid severe near-wellbore problems during hydraulic fracturing stimulation treatments. Since about 2000, and especially during the most recent 5 years, service providers have progressively expanded the processes, which included hydrajet perforating, especially in conjunction with hydraulic fracturing methods. This paper will review the expanding applications of hydrajet perforating in recent years, including case histories from several global applications. Background Early technical papers tell us that hydrojetting (w/o abrasives) was used with acidizing and fracture acidizing as early as 1939, primarily in zones completed open hole. However, with the incorporation of solid abrasives (hydrajetting, using abrasives) the jetting nozzles in use then could only perform for minutes before excessive erosion became a problem. The literature also reveals that around 1958 there was a renewed interest in sand-jetting and more abrasion-resistant carbide jets were developed. In May, 1961, the Journal of Petroleum Technology included three landmark publications that presented much of what had been happening since 1958 with respect to HP applications, and described other hydrajetting wellbore functions such as jetting cement from casing, cutting casing, scale removal, and other applications. The more extensive of these publications (Brown et al. 1961, and Pittman et al. 1961) had first been presented at technical conferences in October, 1960. The shorter, introductory article (Ousterhout 1961) indicated that by early in 1961 over 5,000 hydrajetting jobs had been performed with a success rate in excess of 90%; more than half of these were perforating applications. At that time, explosive/shape charge perforating was still in its infancy, with bullet perforating still common.
This case history paper presents fracture stimulation using coiled tubing (CT) hydrajetting, followed by (1) annular-path pumping of the fracturing treatment and (2) use of high-concentration proppant slugs to create proppant plugs for diversion. The process of hydrajet perforating and annular-path pumping (HPAP) has been used effectively for vertical well completions and is especially applicable for multi-interval completions. Further, use of this process for multi-interval fracturing of horizontal well completions has been performed successfully in several North America reservoirs, and in Texas at depths below 15,700 ft true vertical depth (TVD) and measured depths (MD) of more than 16,700 ft. Cased and cemented horizontal completions present several challenges for the HPAP method, including (1) unique CT calculations and operating procedures, and (2) proppant plug-setting procedures. This multi-stage completion process can also be applied in other methods of horizontal completions that incorporate a solid liner. Several case histories are examined to (1) highlight lessons learned in performance of this method on horizontal well completions, and (2) demonstrate efficiencies gained as compared to following conventional practices. Introduction Fracturing methods aimed at improving operational efficiency by reducing nonproductive time (NPT) have increased in importance as assets are being completed that involve multiple intervals, thick pay intervals, or horizontal wellbores (McDaniel 2005). Some of these methods, such as the use of high fracturing rates and limited-entry perforating, greatly reduce the overall completion time but have been shown to be less than adequate in stimulating all targeted intervals (Craig et al. 2005). Other fracturing methods that focus on treating intervals individually can result in many hours of NPT mainly as a result of discrete process steps that require trips in and out of the well between treatments while pumping equipment resources remain idle or are required to leave and return to the wellsite. These discrete steps include trips for (1) perforating, (2) setting or moving tools such as bridge plugs, and (3) wellbore cleanouts. In the late 1990s, a hydrajetting process (Surjaatmadja 1998) called hydrajet-assisted fracturing (HJAF), using dynamic diversion, was introduced to the industry as a means of treating horizontal wells, in particular openhole horizontal completions (Surjaatmadja et al. 1998; Love et al. 1998; McDaniel et al. 2002). The benefits of this process for reducing NPT were readily apparent and horizontal completions involving 20 separate fracture treatments in a single well have been performed in just 2 days of daylight operation (East et al. 2004). The process uses hydrajet perforating and HJAF, which eliminates a separate trip into and out of the wellbore (Fig. 1). The numerous advantages (and some limitations) of using hydrajetted perforations instead of explosive/shape charge perforating has been recently reviewed extensively in a recent paper (McDaniel et al. 2008). Because the HJAF process relies on dynamic diversion, no mechanical plugs are required to furnish diversion between intervals being treated. Therefore, there is no drilling of plugs or plug-retrieval operations after the treatments have been performed, further reducing NPT in the completion process. The HJAF method allows for recovery from premature screenouts because tubulars are in position for rapid cleanout of excess proppant at each stage of the fracturing and perforating process. This is particularly beneficial when aggressive proppant schedules are required, such as in the case of frac-pack or tip-screenout treatment designs.
Total operates an offshore oil field approximately 60 Km West of Pointe-Noire, Republic of Congo. To date, the Albian reservoir has contributed most of the oil produced. However, a significant part of the oil in place is in the Cenomanian, a low permeability sandstone formation with poor quality. As of early 2007, only two of the initial 50 wells in the field had been completed in the Cenomanian. It was desired to evaluate the potential of hydraulic fracturing stimulation treatments to more fully comprehend the production capability of this reservoir. In early 2007, a third well was drilled and completed in this structure, penetrating the Cenomanian at a 60 degree inclination for this purpose. Proppant fracturing from a wellbore with a 60 degree inclination in a hard-rock formation has always been difficult. Also adding another level of uncertainty was the fact that the Cenomanian has never been fracture stimulated. This paper will detail the planning process from both the operator and the service provider perspectives with specific well control issues related to an over-pressured reservoir. Review of the well conditions and operational constraints indicated the best approach would be a multi-stage pinpoint stimulation method incorporating hydrajet perforating and sand plug isolations using a stimulation vessel especially designed for such work. Additionally, a comprehensive review of the actual three-stage stimulation treatments will detail the perforating, fracturing, and sand plug isolation after each stage. With BH memory gauges just below the jetting tool assembly, post-frac reviews of downhole pressure data is compared with the live annulus data used for real time decisions during the stimulation stages. Post-frac well cleanup and early production data will be included. Background Of the initial 50 wells in the field, only two producers were completed in the Cenomanian instead of the Albian reservoir. Although this reservoir constitutes a major part of the oil reserves of the field, its low permeability (10mD) and poor formation quality (argillaceous siltstones) always result in a low production index in perforated cased hole configuration. To show that a field development on such a reservoir could be economic, it was needed to prove that effective fracturing operations could be performed on the third well, drilled early in 2007, in this structure. No similar operation had been undertaken in West Africa on a hard low perm rock where the core samples appear to come from a well in Texas, instead of offshore West Africa. Furthermore, a fines stabilizer chemical agent was pumped to provide a treatment solution to lock the migrating fines in place to minimize the potential damage to the formation and maintaining the production flow rates of the well. This offshore field is currently operated from two primary platforms set in about 140 m of water. Most of the oil production has been from the 48 wells completed in the Albian reservoir. This reservoir, below the Cenomanian, is a moderate permeability carbonate formation with a varied degree of natural fracturing present. It is typically completed using a large volume HCl acid-frac stimulation after perforating. These wells account for more than 97% of the pre-2007 production of the field What enhances the value of the Cenomanian formation as a producing reservoir (while increasing the complexity of drilling and completion operations) is that this reservoir is significantly overpressured. The reservoir pressure in these zones required the use of a 1.40 sg completion fluid (mixed CaCl2 / CaBr2 brine) to maintain 8 bar over-pressure above reservoir pressure.
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