The SPE has split the former "Management & Information" technical discipline into two new technical discplines:
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The SPE has split the former "Management & Information" technical discipline into two new technical discplines:
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Xin, Haipeng (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology) | Zeng, Jianguo (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology) | Deng, Qiang (PetroChina Tarim Oilfield Company) | Wang, Jianyao (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology) | Shi, Linglong (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology) | Zou, Jianlong (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology)
ABSTRACT CO2 and H2S corrosion resistant cementing systems are widely studied, however, most of them based on oil cement could only reduce corrosion rate rather than eliminate it. A novel CO2 and H2S corrosion resistant calcium phosphate cement was developed to eliminate corrosion. After cured at 100 °C with 5 MPa CO2 for 28 days, compressive strength of calcium phosphate cement set increased to 33.9 MPa from 21.8 MPa while permeability decreased to 0.02 mD from 0.03 mD. Thermal analysis shows that less than 1% weight loss at 600–770 °C which is the decomposition temperature of calcium carbonate indicates that calcium phosphate cement performs good CO2 corrosion resistance. Meanwhile, cured at 80 °C with 2 MPa H2S for 28 days, compressive strength increased to 19.8 MPa from 14.2 MPa while permeability remained unchanged. Calcium phosphate slurry performs good rheology behavior, little liquid loss, rapid ultrasound and static gel strength. The comprehensive performance of calcium phosphate cement could meet the requirement of long-term sealing of cement sheath in CO2 and H2S rich wells. INTRODUCTION CO2 and H2S are common gases in oil and gas development (Li, 2016; Moroni, 2008; Omosebi, 2017; Qiu, 2012; Zhang, 2011), and destroy the seal integrity of the cement sheath leading to annulus pressure (Garnier, 2012). After the structure of the cement sheath is damaged, CO2 and H2S will also directly corrode the pipe string (Kiran, 2017). Moreover, due to the sulfide stress corrosion cracking, the downhole pipe string will suddenly and brittlely break even when the stress is still much lower than its yield strength. If the pipe string or whole well is discarded, H2S will cause huge damage to people, equipment and environment around the well. Due to unqualified cementing quality, severely corroded casing and failed interval plug lead to oil revesed out from the casing and sulfur water coming out of the ground of well R22 in Rumaila Oilfield of Iraq illicit great environmental, safety and security risks to its nearby area. Thus, abandonment operation was carried out (Zhang, 2015). Therefore, in order to prevent formation fluids containing CO2 and H2S from corroding casings and accessories, the first problem to be solved is the corrosion protection of cement sheath.
Milsom, John (1Gladestry Associates, Gladestry, Powys, UK) | Roach, Phil (2Approach Geophysics Ltd, Salford, Oxfordshire, UK) | Toland, Chris (3Oolithica Geoscience Ltd. Cheltenham, Gloucestershire, UK) | Riaroh, Don (4Bahari Resources Limited, Nairobi, Kenya) | Budden, Chris (4Bahari Resources Limited, Nairobi, Kenya) | Houmadi, Naoildine (5Bureau Geologique des Comores, Moroni, Union of the Comoros)
ABSTRACT As part of an ongoing exploration effort, approximately 4000 line-km of seismic data have recently been acquired and interpreted within the Comoros Exclusive Economic Zone (EEZ). Magnetic and gravity values were recorded along the seismic lines and have been integrated with pre-existing regional data. The combined data sets provide new constraints on the nature of the crust beneath the West Somali Basin (WSB), which was created when Africa broke away from Gondwanaland and began to move north. Despite the absence of clear sea-floor spreading magnetic anomalies or gravity anomalies defining a fracture zone pattern, the crust beneath the WSB has been generally assumed to be oceanic, based largely on regional reconstructions. However, inappropriate use of regional magnetic data has led to conclusions being drawn that are not supported by evidence. The identification of the exact location of the continent-ocean boundary (COB) is less simple than would at first sight appear and, in particular, recent studies have cast doubt on a direct correlation between the COB and the Davie Fracture Zone (DFZ). The new high-quality reflection seismic data have imaged fault patterns east of the DFZ more consistent with extended continental crust, and the accompanying gravity and magnetic surveys have shown that the crust in this area is considerably thicker than normal oceanic and that linear magnetic anomalies typical of sea-floor spreading are absent. Rifting in the basin was probably initiated in Karoo times but the generation of new oceanic crust may have been delayed until about 154 Ma, when there was a switch in extension direction from NW-SE to N-S. From then until about 120 Ma relative movement between Africa and Madagascar was accommodated by extension in the West Somali and Mozambique basins and transform motion along the DFZ that linked them. A new understanding of the WSB can be achieved by taking note of newly-emerging concepts and new data from adjacent areas. The better-studied Mozambique Basin, where comprehensive recent surveys have revealed an unexpectedly complex spreading history, may provide important analogues for some stages in WSB evolution. At the same time the importance of wide continent-ocean transition zones marked by the presence of hyper-extended continental crust has become widely recognised. We make use of these new insights in explaining the anomalous results from the southern WSB and in assessing the prospectivity of the Comoros EEZ.
Abstract Oilfield-cement compositions capable of self-healing cracks/fractures in set cement without depending on contact with a fluid, such as water or oil, have been developed. Traditionally, such compositions include additives that are capable of swelling when exposed to fluids like water or oil, for example. Presumably, if the cement develops cracks/fractures or flow channels caused by shrinkage or debonding and allows fluid flow, the swelling additive exposed to such fluids will swell, thereby healing the flow path. The current technology employs additives that swell either in water or oil, but not both. Such additives do not swell when exposed to gas, irrespective of whether the gas is carbon dioxide or a hydrocarbon. Dependence on additives to swell and block flow channels after contact with a specific type of fluid hinders the self-healing effectiveness of the cement composition. As a result, designing cement compositions for field applications requires prior knowledge of the type of fluids that the cement may come into contact with, not only through the productive lifetime, but also after abandonment of the well. Alternately, multiple additives that will swell and seal in both water and oil might need to be included in the initial cement design. Even in the latter case, the compositions still cannot offer protection against gas flow. A new class of elastomeric additives that do not depend on the nature of fluid to seal cracks is presented in this paper. Performance of these additives in a variety of self-healing tests based on flow studies through cracked cement cores will be presented. In addition, the importance of specific structural features of the additives that render them suitable for inclusion in self-healing cement compositions will be discussed. Introduction A cement column in a wellbore is subjected to external and internal stresses beginning at the time a wellbore portion is cemented and throughout the well completion, production, perforation, stimulation, and remedial operations. These stresses have the potential to induce cracks in the cement column and create microannuli unless the cement is designed to withstand such imposed stresses. As a result, the cement sheath might lose the capability to provide the intended zonal isolation, resulting in problems, such as sustained casing pressure (SCP) and interzonal communication, caused by flow of fluids through the flow paths created by cement failure. There are many instances worldwide of SCP in abandoned and newly completed wells. The cost to the operator of monitoring and maintenance in the former case, and repair by squeeze cementing, for example, in the latter case is substantial. A recent approach to solving the problem is to alter the mechanical properties of cement compositions based on computational methods so that the cement sheath can withstand imposed stresses throughout the life of the well. So far, this approach appears to be successful, although it remains to be seen whether zonal isolation in such wells will continue to be effective for the remainder of life and after abandonment. Another recent approach has been to design cement compositions capable of self-repairing when the cement sheath fails because of development of cracks or microannuli from debonding (Ravi and Darbe 2007; Cavanagh et al. 2007; Moroni et al. 2007; Bouras et al. 2008; Roth et al. 2008). Cement compositions designed to self-repair are also referred to as self-adaptive, self-healing, and, in the construction industry, as autogenous-healing cements. Cement compositions for oilwell cementing contain additives that swell on exposure to either aqueous fluids or hydrocarbons, including oil and gas, and seal off any fluid-flow paths (Le Roy-Delage et al. 2007a; Le Roy-Delage et al. 2007b; Mueller, 2008). Additives that swell in aqueous fluids are typical superabsorbents similar to those used in the hygiene industry, whereas those that swell in hydrocarbons include elastomers, hydrophobic polymers, and acrylates, etc. Many field jobs performed with cement compositions containing additives that swell in hydrocarbons have been performed with apparent success, at least in the short-term, even in gas fields. In the construction industry, cement compositions containing crack-filling and healing materials encapsulated in hollow fibers have been proposed in patent literature (Dry 2003 and 2006; Li and Yang 2008). It is presumed that the fibers will break when the cement cracks, releasing the sealant material into the cracks.
This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 112313, "Manganese-Tetraoxide-Weighted Invert Emulsions as Completion Fluids," by L.P. Moroni, SPE, J.R. Fraser, and R. Somerset, Baker Hughes; A. Jones, Oilexco North Sea; and A. Guarneri, Eni AGIP SpA, originally prepared for the 2008 SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, 13-15 February. The paper has not been peer reviewed. Traditionally, completion equipment is run in clear fluids, brines, or base oils to minimize the potential for solids to plug equipment. Base oils typically have approximately 0.8 specific gravity (SG), which has well-control implications, and brines can be prohibitively expensive where high densities are required. A novel approach was used by a UK operator to address these problems by compromising between the shale stability provided by oil and the density achievable with brine. Introduction Once the drilling phase is complete, most operators clean up the well before running the completion string. With non-aqueous fluids (NAFs), cleanup can be quite complicated, requiring a sequence of surfactant pills to remove mud residue from the wellbore and casing. The objective is to leave the well with a clean fluid that has very-low solids content (typically less than 0.05%) or meets a clarity specification. This process can result in large volumes of fluid that are considered to be contaminated to the point of requiring disposal. Where an NAF is used, environmental limitations usually require the contaminated fluid to be contained for special disposal. Manganese tetraoxide (Mn3O4) has been used as an alternative weighting agent in both water-based and nonaqueous drilling fluids where equivalent circulating density and sag performance have precluded use of barite-weighted fluids. The combination of small particle size, spherical shape (Fig. 1), and high SG (4.8 g/cm) makes Mn3O4an ideal weighting agent for fluids in which a low viscosity profile and low gel strength are required. Case History 1 A temporary completion fluid with 1.95 SG was required while running the completion string to provide a secondary well-control barrier in addition to the cemented liner while the blowout-preventer (BOP) stack was replaced with the Christmas tree. Use of cesium formate was one alternative explored by the operator, but the cost was considered prohibitively high. A previous application that used a water-based mud containing ultrafine barite failed on three issues: The fluid was prone to barite sag, the fluid left a coating on tubulars that was virtually impossible to remove, and the fine barite particles plugged surface well-test-line valves. One of the major concerns was the tight clearance (0.1 in.) of the hydraulically set packer and the risk of setting prematurely because of pressure surges while displacing to the oil-based packer fluid. The wellbore geometry consists of a long tangent between 40 and 50º, so sag prevention is a key requirement.
Abstract The wells in the Tuscaloosa trend in South Louisiana are high-pressure high-temperature (HPHT) wells reaching as deep as ±23,000 ft, with a bottomhole static temperature (BHST) as high as ±400°F. In the past these wells were completed using conventional cementing techniques. In some cases, soon after the wells were put on production, the intermediate casing annulus would show an increase in pressure. Historically, this pressure is manageable and can be easily reduced through current procedures and practices. However, a project was undertaken to understand the underlying cause and then subsequently deploy a solution to prevent pressure on the annulus side. The first task was to make sure that the annulus pressure was not caused by other problems such as wellbore stability, hole cleaning, and cement slurry placement. Then the next possible cause was damage to the cement sheath during subsequent well operations and production. A detailed study was done to investigate this possibility. Mechanical and thermal properties of the formation were derived from the log data and drilling data. Additionally, this data was evaluated to identify the depths and formations associated with significant gas shows at surface. Possible failure mechanisms in the previous conventional cement sheath were identified. The cement system was modified to prevent such failure and the new cement system was designed and tested. The modified cement system was deployed in the field in April 2006, and the well was put on production a few months later, and since then has been on line and producing without annular pressure problems. The techniques and solutions discussed in this paper can be applied to wells around the globe that have related problems. These solutions may help prevent annular pressure and improve the safety and economics of operating these wells. Introduction The cement sheath in the annulus is an important barrier that helps prevent formation fluid from entering the annulus and thus helps maintain well integrity. Well integrity could be compromised if the cement sheath is not able to withstand well operations and is damaged during the life of the well (Bosma et al. 1999; Fourmaintraux et al. 2005; Ravi et al 2002). This could result in tubular corrosion, interzonal communication, and annular pressure buildup and lead to an increase in operating costs and unsafe well conditions. In the worst case, the compromised well integrity may lead to casing collapse or a well blowout. There are compelling reasons to design and deliver a cement slurry that is placed in the entire annulus and to ensure that the cured cement sheath is not damaged during well operations. The general cementing practice in the industry has not considered the effect of well operations on the cement sheath during the life of the well. It is only recently, and only in a handful of wells the cement sheath integrity during well life has been considered as a design parameter. The results show that, in cases where the cement sheath integrity during well life is taken into account, there has been marked improvement in well performance. The operating cost of these wells has decreased while the long term integrity of the well leads to safer operating conditions (Heathman et al. 2006; Hunter et al. 2007; Moroni et al. 2008).
This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 110523, "Overcoming the Weak Link in Cemented Hydraulic Isolation," by N. Moroni and N. Panciera, Eni E&P; A. Zanchi, Stogit; and C.R. Johnson, SPE, S. LeRoy- Delage, SPE, H. Bulte-Loyer, SPE, S. Cantini, SPE, E. Belleggia, SPE, and R. Illuminati, SPE, Schlumberger, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11-14 November. The paper has not been peer reviewed. The full-length paper describes a unique isolation solution based on a responsive cement system with intrinsic self-healing properties that are activated automatically upon hydrocarbon exposure. Activation occurs whenever the integrity of the cement sheath is compromised. The new sealant system rapidly forms a complete barrier by swelling and continues to reseal should further damage occur. The technical advantages of this sealant have been demonstrated through successful field tests. New Sealant System In recent years, the well-cementing industry has begun to concentrate on the ability of set cement to provide zonal isolation throughout the lifetime of the well. Even if the cement has been placed properly and initially provides a competent hydraulic seal, zonal isolation could be compromised as a result of changing downhole conditions over the lifetime of the well. Studies have shown that the main causes of cement-sheath damage are stresses induced by varying downhole conditions. The loss of zonal isolation after cement has hardened can be a result of mechanical failure of the set cement itself or debonding of the casing from the cement or the cement from the formation. Several solutions have been developed and applied successfully in field applications. One current method to improve cement resistance to physical stresses involves the addition of fibrous or ribbon-like materials to increase the toughness of the cement matrix. While these methods increase the resistance of the cement matrix to physical stresses, none of these approaches can accommodate problems that occur once the cement sheath has actually failed and becomes permeable. The objective of the self-healing cement (SHC) system is to pro-vide long-term zonal isolation with a cement-based system that incorporates self-healing additives. Hydrocarbons activate the self-healing additives whenever the integrity of the cement sheath is compromised (e.g., cracks and micro-annuli), and the cement matrix would seal the leak path through a swelling mechanism. Application of this responsive sealant targets a wide range of wells to mitigate risks of future cement-sheath degradation through unplanned well events and operations, and to ensure long-term zonal isolation throughout the productive and abandoned periods. The versatile sealant can be strategically placed, from surface to total depth of the well in any string of the well, to provide an effective long-term seal.