A PDC Solution to Drilling Sticky Formations With Noninhibited Water-Base Drilling Fluid: Experience in the Provincia Field in Colombia
Abstract: This case history documents the successful drilling of sticky clays, clay-stones and shales with non-inhibited, water base drilling fluid using a Polycrystalline Diamond Compact (PDC) bit designed specifically for this application. In the Provincia field of Colombia, where sticky clays, claystones and shales present just this sort of problem, a fishtail-style PDC bit has been found to be the best solution to date to drill these formations. It's use has resulted in a reduction in drilling time per well in this … Show more
Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
Cited by 5 publications
References 2 publications
Wells drilled in the Andean Mountain region of South America present significant challenges as a result of both operational and environmental factors. Wells located in the foothills along the basin are particularly difficult due tectonic stresses and unstable, probably, micro-fractured shales. Operators have experienced difficulties drilling wells using both water-based and oil-based muds (OBM). Environmental regulations hinder the use of OBM in many of those areas due to the potential environmental impact and costs associated with waste disposal. In many cases OBM has not prevented wellbore instability problems. This paper explains how a lack of understanding of regional geology and the practice of using successful drilling fluid design and drilling practices from other areas has led to wellbore problems. The water phase salinity of OBM and the use of the appropriate inhibitors in the drilling fluid play a key role in the minimization of wellbore problems. Although reactive clays are present in all the shales along the basin, they represent only 30 to 40 percent of the clay fraction, while non-expandable kaolinite clays are the major clay components. This paper explains how physical/mechanical effects are more important than inhibition in controlling these shales. Moreover, in some cases "excessive inhibition" due the presence of shale inhibitors such us potassium and high water phase salinity in OBM exacerbate the problems. Pore pressure transmission caused by fluid invasion is a major contributor to the observed problems. A combination of operational practices and improved fluid design minimizes mud and filtrate invasion. Troublesome shales in the Andean basin include, from north to south, the La Rosa and Icotetea in Venezuela, the Carbonera, Leon and Villeta in Colombia, the Napo in Ecuador, the Chonta in Peru and the Los Monos in Bolivia and Argentina. Case histories involving these shales are presented. Contrary to experiences in many other parts of the world, high water phase salinity OBM and potassium based water-based mud (WBM) are not the answer to shale stability problems. Rather, mud sealing properties, correct chemical composition and appropriate drilling practices are the key factors in maintaining wellbore stability. Introduction The challenges of drilling in the Andean Mountain region of South America are well documented. The presence of tectonic stresses combined with over pressures1 makes this a particularly challenging region. The stresses in this region were generated by the Andes Mountain orogeny. The geology is typified by steeply dipping sand/shale sequences. Many faults have been documented in this area. Claystones and shales dominate the lithology in this region. These clays and shales can be "sticky"2 at times, requiring the use of inhibitive drilling fluids to minimize the associated problems. The factors discussed above lead to wellbore stability being a major challenge when drilling in the Andean mountain region. These problems present the greatest challenge when drilling directional wells3. The drilling problems experienced in Colombia are well documented and include stuck pipe, high torque and drag, tortuous wellbores, twist-offs, poor cementing, and unplanned back-offs. Many of the difficulties encountered have been attributed to poor hole cleaning in enlarged hole resulting from wellbore instability. The cavings generated during the hole enlargement process have also presented hole cleaning challenges. Success in drilling wells in this region has been attributed variously to simplifying well design, understanding the tectonic stresses and their orientations, drilling fluid design4 and sound drilling practices.
Wells drilled in the Andean Mountain region of South America present significant challenges as a result of both operational and environmental factors. Wells located in the foothills along the basin are particularly difficult due tectonic stresses and unstable, probably, micro-fractured shales. Operators have experienced difficulties drilling wells using both water-based and oil-based muds (OBM). Environmental regulations hinder the use of OBM in many of those areas due to the potential environmental impact and costs associated with waste disposal. In many cases OBM has not prevented wellbore instability problems. This paper explains how a lack of understanding of regional geology and the practice of using successful drilling fluid design and drilling practices from other areas has led to wellbore problems. The water phase salinity of OBM and the use of the appropriate inhibitors in the drilling fluid play a key role in the minimization of wellbore problems. Although reactive clays are present in all the shales along the basin, they represent only 30 to 40 percent of the clay fraction, while non-expandable kaolinite clays are the major clay components. This paper explains how physical/mechanical effects are more important than inhibition in controlling these shales. Moreover, in some cases "excessive inhibition" due the presence of shale inhibitors such us potassium and high water phase salinity in OBM exacerbate the problems. Pore pressure transmission caused by fluid invasion is a major contributor to the observed problems. A combination of operational practices and improved fluid design minimizes mud and filtrate invasion. Troublesome shales in the Andean basin include, from north to south, the La Rosa and Icotetea in Venezuela, the Carbonera, Leon and Villeta in Colombia, the Napo in Ecuador, the Chonta in Peru and the Los Monos in Bolivia and Argentina. Case histories involving these shales are presented. Contrary to experiences in many other parts of the world, high water phase salinity OBM and potassium based water-based mud (WBM) are not the answer to shale stability problems. Rather, mud sealing properties, correct chemical composition and appropriate drilling practices are the key factors in maintaining wellbore stability. Introduction The challenges of drilling in the Andean Mountain region of South America are well documented. The presence of tectonic stresses combined with over pressures1 makes this a particularly challenging region. The stresses in this region were generated by the Andes Mountain orogeny. The geology is typified by steeply dipping sand/shale sequences. Many faults have been documented in this area. Claystones and shales dominate the lithology in this region. These clays and shales can be "sticky"2 at times, requiring the use of inhibitive drilling fluids to minimize the associated problems. The factors discussed above lead to wellbore stability being a major challenge when drilling in the Andean mountain region. These problems present the greatest challenge when drilling directional wells3. The drilling problems experienced in Colombia are well documented and include stuck pipe, high torque and drag, tortuous wellbores, twist-offs, poor cementing, and unplanned back-offs. Many of the difficulties encountered have been attributed to poor hole cleaning in enlarged hole resulting from wellbore instability. The cavings generated during the hole enlargement process have also presented hole cleaning challenges. Success in drilling wells in this region has been attributed variously to simplifying well design, understanding the tectonic stresses and their orientations, drilling fluid design4 and sound drilling practices.
Summary. This paper presents the results of a recent study conducted to determine application and operating requirements for polycrystalline diamond compact (PDC) bits in the Gulf of Mexico. This study evaluated PDC-bit usage in Miocene sections of the Gulf of Mexico and has resulted in a saving of more than $1.4 million based on 22 bit runs. As a result of this study, operational guidelines for PDC bits were established and drilling costs per foot were significantly reduced. In addition, a relationship was found between shale reactivity, strength, and density. This proved to be an effective aid in bit selection and determination of hydraulic requirements and verified the results of the study. Introduction While a well is being drilled, the rate of penetration (ROP) usually decreases with depth. ROP's with conventional rock bits are affected by tooth and bearing wear, whereas PDC bits are minimally affected. On the basis of advances made with PDC bits and new failure-mechanisms theories, PDC bits have successfully reduced cost per foot in basins outside the Gulf of Mexico.A majority of the footage drilled in the Gulf of Mexico was with rock bits. Past PDC applications were limited primarily to deep hole sections, smaller hole sizes, or wells drilled with oil-based muds. It was recognized that rock mechanics laws did not support the previously mentioned PDC limitations. PDC bits should out-perform rock bits because most shales fail easily in shear and PDC bits always operate in a shearing mode. in addition, PDC bits are known to drill better in water-based muds when shale shear strength is high. A paradox between physical law and practice existed. A more thorough understanding of the effect of mud type, formation composition, and hydraulics would be required to find a solution.A study was initiated in May 1985 to determine how to apply PDC technology in the Gulf of Mexico. The Tenneco Real Time Data Center was used to monitor and to collect drilling data for this study. This also allowed bit performance to be related to lithology and electric log data. The runs were made in a water-based drilling fluid with large- diameter cutter- and fishtail-type PDC bits. Typical savings, vs. those with conventional milled-tooth rock bits, ranged from $30,000 to $90,000 per run. The longest continuous run was 5,685 ft [1733 m] (6,665 ft to 12,350 ft [2031 to 3764 m]) at an average ROP of 90 ft/hr [27 m/h] (Table 1). The success experienced on these PDC bit runs was a result of matching proper bit design and hydraulics to formation composition, using the relationship between shale reactivity and bit performance. This paper examines the relationship between these previously mentioned variables with respect to PDC performance. It will also address design and operational considerations essential to successful water-based PDC applications in the Gulf of Mexico. Theorized Rock-Failure Modes The manner in which a rock fails is important in bit selection. This failure mode can be brittle or plastic depending on the confining stress. Conventional theories used in the calculation of confining stress assumed that the pore pressure within shale remained constant. If this were true, however, it is unlikely that the confining stresses would be high enough to cause the shale to become plastic. Recent data and rock failure theories support the position that most shales fail in a plastic condition. This plasticity was confirmed from field data.A theory explaining this behavior was presented in a paper by Warren and Smith, which examined localized stress conditions at the bit. This theory is predicated on stress relieving the original shale, which causes a PV increase. This stress relief is caused by replacement of the heavier overburden with a lighter mud. This is normally the case because most mud weights are less than 20 lbm/gal [less than 2397 kg/m3], which approximates overburden density. Because shale is impermeable, there is no pressure maintenance through fluid movement, and because the of PV increase, some pore-pressure loss is expected. This localized loss of pore pressure will increase confining stress on the shale near the bit. The magnitude of the confining stress depends on the fluid type trapped in the shale. If a compressible fluide.g., gasis contained in the pore spaces, the pore-pressure loss within the shale will be insignificant, If an incompressible fluide.g., wateris contained in the pore space, a significant amount of the original pore pressure is lost. This results in very high localized confining stress and causes the mechanical properties of the shale to change. This phenomenon is modeled with a Mohr envelope. Because these theories have established that most shales are plastic and fail easily in shear, it follows that a PDC bit, which is a drag-type bit, should be the optimum bit to use. Bit-Design Characteristics For the purpose of this study, PDC bits are broken down into three general classes:conventional PDC bits made with 1/2-in. [1.27-cm] cutters found on familiar diamond-bit profiles (Fig. 1),fishtail PDC bits made with 1/2-in. [1.27-cm] cutters on historic fishtail drag-bit profile (Fig. 2), andlarge-cutter PDC bits made with large (1, 1 1/2-, or 2-in. [2.54-, 3.81-, or 5.08-cm] -diameter) cutters with a nozzle for each cutter (Fig. 3). There are several styles with each of the three classes of bits, but all styles within a class will exhibit similar features in terms of overall design variables. The following general design variables are considered: Cutter Exposure. Exposure is defined as distance of the bit face to the cutter tip. Exposure can be achieved either with cutter size or with a structure on the bite.g., steps and blades-to elevate the cutters above the rest of the bit face. Conventional PDC bits used as a baseline show how the other two bit classes achieve an increase in cutter exposure. Fishtail bits use a drag blade, or exaggerated junk slot, to elevate the cutters from the bit body. Bits with large-diameter PDC cutters use the cutter size to increase the exposure. Profile. Profile is the shape of the bit or the structure on which the cutters are placed. Figs. 1 through 3 show a variety of profiles within each class. SPEDE P. 117^
CopvrIght -7, Society of '-Iroleum Ingl_ _This paper was prepered lor presentation at Offshore Europe 87, Aberdeen, 8-" september, 1987 Permission to copy is restricted to an abstract of not more than 300 words. lIIustretions may not be copied. The abstract shouldcontain conspicuous acknowledgement of where and by whom the papar was~ted. Publication elsew1'er8 is usuelly granted upon request provided proper credit is made. ABSTRACTA description is given of a single-cutter tester for studying ,the cutting process of PDCs in rock under simulated downhole conditions. The use of the tester is illustrated by a study of the effect of downhole pressures on the cutting process in shales. Prior to the tests the Pierre shale and Mancos shale outcrop samples used for the study were conditioned to enable proper downhole pressures to be simulated during the tests.The total bottomhole pressure only was found to govern the cutting process in Mancos shale, whereas both the pore pressure and the total bottomhole pressure govern the cutting process in Pierre shale. The dilatancy characteristics of the rocks are shown to be responsible for this behaviour. In addition the tests unveiled the balling mechanism of the outcrop shales in water-based and oil-based mud environments.On the basis of the insight gained from single-cutter tests, the paper discusses drilling characteristics of PDC bits in shales and bit and cutter design aspects that facilitate mechanical bit cleaning as a means of improving POC bit performance in various shales.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
Contact Info
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Product
Resources
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.
