Bottom-hole assembly (BHA) drill stem components and tools are heavy and have increased wall thickness compared to drill pipe. These components are typically run in compression, which can result in buckling, subjecting the BHA components to bending. Rotation under bending creates cyclic stress, fatigue, and can lead to possible failure. Changes in cross section and the presence of sharp corners and geometric discontinuities in the BHA thread/connection profile produce a higher localized stress state, a stress concentration, in comparison with the tube body of the BHA component. As a result, the connection is almost always the point of fatigue failure in drill collars (DC) and the point of failure in heavy weight drill pipe (HWDP) about half of the time. Therefore, increasing the fatigue life of the connection is beneficial. To increase BHA connection fatigue life, stress reducing features such as pin stress relief grooves, box borebacks, and a cold-rolling of the thread roots (creating a compressive stress state) have been incorporated into BHA connection design.
Additional connection designs have been developed that provide additional stress reduction and extend the connection fatigue life. Besides improving the resistance to fatigue crack initiation, these designs provide an added benefit of reducing the material loss when repairing (recutting) the connection. Three different field proven connection technologies are presented in this paper. The connection features that contribute to improved fatigue performance are described. The first is a modification to an API rotary shouldered connection. The second is a proprietary double-shoulder connection developed specifically for BHA tools. The benefits of both are discussed, including the results of full-scale comparative fatigue testing. The amount of material loss from repairing the connection and the impact on product life are also examined. Third, the use of streamline proprietary double-shouldered connections on heavy weight drill pipe (HWDP) is discussed. Recommendations are presented.
Carbonated Water Flooding (CWF), an alternative enhanced oil recovery (EOR) method in which an oil reservoir is flooded with CO2-enriched water, can be considered as a promising solution for mobilization and recovery of residual oil in water wet rock. At the same time it is a possible mitigation option for an increasing CO2 concentration in the atmosphere and an opportunity for permanent and safe disposal of CO2 underground. One of the important aspects of the CWF process is molecular diffusion of CO2 from carbonated water into oil (DCWO). The process benefits from oil viscosity reduction, an increase in oil relative permeability and, as a result, enhancement of oil mobility. In contrast to many previous studies on the diffusion of carbon dioxide directly into oil by CO2 flooding, DCWO characterization is underexposed in laboratory work and literature. In order to understand the distribution of the total dissolved CO2 between the coexisting phases water and oil, we examine DCWO in experiments by visualization of oil swelling and recovery over time.
To determine the phase behavior of the system, pore-scale diffusion experiments are conducted. In these experiments oil is initially placed in a dead-end pore and covered with water presumed to be from the first secondary recovery phase. Swelling of oil due to CO2 diffusion from a CO2 source, either a CW stream or a pure CO2 stream under P, T-conditions, have been recorded and visualized over time. As a result, pressure and oil-composition dependent, recovery of oil occurs. Based on the results we determined a dominant role of diffusion in the CW recovery process. Existence of ample contact time for water rupture was obtained. In the pore scale water barrier, its geometry (especially - the interfacial area) appears to be a limiting factor. At field scale, time in the range of hours does not play an important role in the overall recovery; however it is of importance for near well injection area.
The results and visualizations of the conducted experiments will contribute to a better understanding of processes such as molecular diffusion in CWF, which will occur. In addition, DCWO results lead to process improvements for achieving recovery in both laboratory core floods and in the field, with an option for CO2 sequestration.
In low permeability oilfield, normally fracturing is applied for production and the water injecting pressure is quite high. As most of the major oil reservoirs are flooded by water after fractured, the production rate is very low. With the oilfields further developed, the number of high water cut wells increased. How to further tap the remaining oil and enhance the oil recovery is becoming a big challenge to us currently. In Daqing low permeability oilfield, a pilot test of pressure plugging, water control and oil recovery of high water cut wells was conducted and achieved a good result. The test was including: 1) Further verified the understanding of well and reservoir selection and established the selection standard of the pressure block, water control and oil recovery technique for fractured reservoirs in low permeability oilfield. 2) Optimized field operation process of pressure block, water control and oil recovery. Compensator + K341-114 packer + fixed pressure valve + K341-114packer + ball seat was designed as the plugging string. Small diameter string was studied to repair casing damaged wells. 3) Optimized the chemical plugging agent and developed the fracturing technique of plugging the water cracks through compound water plugging. Production enhancement and water drop were observed through large scale field application.
Li, Qiaoyun (Research Institute of Petroleum Exploration and Development) | Wu, Shuhong (Research Inst. Petr. Expl/Dev) | Wang, Baohua (Research Institute of Petroleum Exploration and Development) | Li, Xiaobo (Research Institute of Petroleum Exploration and Development) | Li, Hua (Research Institute of Petroleum Exploration and Development) | Zhang, Jiqun (Research Institute of Petroleum Exploration and Development) | Meng, Lixin (Research Institute of Dagang Oilfield, PetroChina)
Reservoir numerical simulation, which interests a large amount of reservoir engineers, is an important tool in oilfield development researches. This paper introduces a new generation simulator, which can be used to simulate the traditional and pseudo-compositional reservoirs. This simulator adopts finite volume method, completely implicit time discretization technology (CITDT) and dynamic space discretization technology (DSDT). The multilevel preconditioner solver, which is applied in the simulator, can enhance the computation speed. In this paper, a mature heterogeneous water-flooding oilfield with 30a's development history is simulated by this simulator. In the course of development, there are 242 producers and injectors drilled, and the exploitation strata-series are adjusted frequently. Currently the reservoir has entered the "double high?? stage, more than 79% of recoverable reserves have been produced and the water-cut reaches to 90%. After history-matching and production prediction by this simulator, the results shows that this reservoir numerical simulator can be used to simulate the complex reservoirs with long development history and mounts of wells, and it can describe the production performance precisely. Moreover, the case study indicated that the new generation simulator is a fast and adaptable tool to simulate the complex reservoirs with large scale, which shows its high potentiality in industrial application.
In the search for hydrocarbons, fractured carbonate formation drilling presents significant challenges associated with fluid losses and well control. These challenges also include open-hole formation evaluation. As a result, cased-hole analyses including production logging presented an opportunity to achieve complete formation, pressure and fluid evaluations in these fractured carbonate reservoirs.
In this appraisal case study, it was crucial for the G&G team to evaluate zonal productivity, fluid type, and formation pressure to further manage uncertainties in reserves booking. The target reservoir, which consists of cycle IV and cycle II carbonates, is naturally fractured with significant predicted gas reserves and unknown water contact. The 2nd well in the field has been recently successfully drilled to TD with a combination of conventional drilling with LCM to treat partial losses, and unconventional drilling with Light Annular Material (LAM) and pumping seawater through the annulus when total losses were encountered.
Though drilling was successful in this hostile carbonate environment, the main objective to obtain pressure measurements suitable for gradient analysis in open-hole environment at balance condition has raised uncertainties in their technical validity. Nonetheless, due to high risk of gas migration from fractures, the well needed to be secured immediately right after successful drilling. It was cased with 7?? liner and cemented. This left the operator staging for cased-hole wireline production logging to close the evaluation gaps.
Cased-hole wireline production logging program was designed to help in providing a better understanding on the fluid type, density and zonal contribution. When production log results were combined with cement log evaluations, they revealed important information that helped with better understanding the source of produced fluids beyond the standard production log interpretation. Results also presented lessons learned for future wells to be drilled in similar environment. Field results, challenges and lessons learned will be presented in this work.
In recent years, the low permeability reserves account for over 70% of the annual new reserves of PetroChina. In 2009, the annual producing reserves and the new drilled wells of the low permeability reservoirs accounted for 70% of the total number, respectively. The low permeability and non-conventional reservoirs are characterized by high percolation resistance and poor connectivity, and may yield commercial value only after acidizing or fracturing. However, the production of acidized or fractured vertical wells is still low and the benefit is poor. The horizontal wells have the advantages of large drainage area and low pressure drop, which make the multi-stage horizontal fracturing an effective technology for the development of low permeability and non-conventional reservoirs. Most of the horizontal wells of PetroChina low permeability reservoirs are completed with casings to meet the requirement of water injection, thus the technology of horizontal fracturing in casing is crucial for improving recovery efficiency. Three principal techniques of multi-stage fracturing were developed, i.e., double-packer single-slip, packer-sliding sleeve, and hydraulic sandblast, together with four matching techniques such as multi-stage stimulation with chemical temporary-blocking gel plug, high efficiency self-diverting acidizing or acid-fracturing technique of carbonate reservoir, hydraulic fracture monitoring and evaluation, and horizontal well workover. In addition, an optimization method of fracture and well pattern was also proposed. The 3 principal techniques, 4 matching techniques, and the optimization method, effectively promoted the industrial application of horizontal wells in low permeability reservoirs.
Maintaining verticality in today's challenging drilling applications is of critical concern. The vertical section is increasingly important in anti-collision situations, as well as in extended reach directional wells where weight transfer through tortuous vertical sections can make the difference in calling Target Depth (TD) early of not. Excessive dogleg severity compromises well completion and adds costs that erode the profitability of operations and ultimately production of the well.
To date, a limited number of options have been available, with low cost, low performance systems at one end of the scale and high cost, high performance systems at the other. Every day we are looking at more unconventional reserves and tighter budgets to work within. To align with these goals, we must find a solution that provides the quality performance through a technology that fits today's fiscal demands as well.
Conventional vertical drilling approaches such as control drilling, drilling with bent housing motors, and rotary steerable systems have notable drawbacks. Poor performance and efficiency on the low end and exorbitant cost on the high end push us to a new solution.
A technology is now commercially available that provides all the performance of the higher cost Rotary Steerable System (RSS) while offering a better economic position for operators. With this new technology, borehole quality no longer has to be sacrificed for cost. The technology is fully autonomous and recent performance data shows that a major operator has utilized this technology for a reduction in costs of over 20% versus conventional technology while providing comparable rates of penetration and borehole quality.
Under the conditions of injecting pure CO2, the corrosion rate of strings in CO2 injection wells is very low, while in WAG process, because CO2 is mixed with water, corrosion rate of downhole strings is high. Hence, we need to take some anticorrosion measures. Because of the fluctuations in pressure and the changes in temperature due to frequent changes of gas injection and water injection, both of these two processes will cause load changes of the tubing, as well as reduce the tubing seal behavior. WAG technology should be optimized.
According to affecting factors of corrosion of WAG process in CO2 flooding, studies of corrosion prevention measures of wellhead equipment, downhole strings and casing are carried out. Based on different conditions of string mechanics in the WAG process, considering different working conditions, the CO2 WAG process is optimized to reduce fatigue failure due to the fluctuations of pressure and temperature on the strings.
The safety control technology of CO2 WAG is widely used in CO2 flooding test in Daqingzi oilfield. In the CO2 WAG process, the technology optimizes injection strategy and corrosion prevention measures in CO2 WAG injection process, protects wellhead equipment and downhole strings of the CO2 injection effectively, as well as ensures safe and smooth operation of CO2 injecting wells.
Keywords: CO2 flooding, WAG, Anticorrosion, String mechanics, Safety control
Yinggehai basin is located in South China Sea; it is characterized with high geothermal gradient and high overpressure. Numerous pore pressure predictions with VSP look-ahead have been conducted in this area. As pore pressure prediction with this approach is very sensitive to the inverted VSP velocity, based on our post drill analysis of pore pressure prediction results with VSP look-ahead data, it has been demonstrated that undercompaction is not the only overpressure mechanism in this study area, unloading may also have contributed to the overpressure. Both Bowers and Eaton models can be applied to predict pore pressure ahead-of-bit for the overpressure mechanisms in the area. An error of 5% in VSP-inverted velocity could generate the error in predicted pore pressure approximately 0.16SG based on Bowers model. Therefore, with experiences gained from VSP velocity inversion part, determining the top depth of the high pressure target with the inverted VSP velocity curve is proposed in this study block to allow for an optimal setting depth of the casing shoe. A case study with this approach is presented in this paper.
Carrillat, A. (Schlumberger) | Bora, D. (Schlumberger) | Dubois, A. (Schlumberger) | Kusdiantoro, F. (PT Medco E & P Indonesia) | Yudho, S. (PT Medco E & P Indonesia) | Wibowo, E. (PT MEDCO E&P INDONESIA) | Musri, M. (PT Medco E & P Indonesia) | Tobing, J. C. (PT Medco E&P Indonesia) | Gomez, Pedro (Schlumberger) | Xue, F. (Schlumberger) | Balasejus, D. (Schlumberger) | McDonald, T. D. (Schlumberger) | Audemard, P. (Schlumberger)
South Sumatra Basin is an inverted post-arc Tertiary basin, which has a complex evolution history from late Eocene-Oligocene extension to late Miocene and Pliocene compression. To evaluate the overall basin prospectivity, a regional analysis is conducted at 8 stratigraphic levels from pre-Tertiary unconformity to Pleistocene. An integrated interpretation including more than 1400 2D seismic lines, 4 seismic 3D surveys, and formation evaluation from 80 key wells is used to run the basin analysis. A series of regional seismic transects are defined through key wells and major structural elements to capture the characteristics of structural styles, lithostratigraphy and hydrocarbon distribution across the basin.
Structural restorations unravels the timing of fault activity showing basin rifting until ~23 Ma with main depocenters in Benakat Gully, Limau Graben, Central Palembang and Lematang Depression followed by sagging until 14.6 Ma. The compressive event is recorded from 5 Ma to present day. The buckling of syn-rift sediments suggests shortening expressed by inversion and fault reactivation rather than thrusting. Review of the source rock data, reservoir distribution, hydrocarbon phase and source to reservoir correlation data are evaluated in perspective of the basin configuration in order to select sections for basin modeling. The modeling results show onset of expulsion varying from ~10-15 Ma from Lemat Fm. and Talangakar Fm., and 5 Ma from Telisa Fm. Modeling suggests that Talangakar Fm. reservoirs are completely filled, whereas Lemat Fm. reservoirs are partially filled due to limited lateral and downward migration. Baturaja Fm. reservoirs in proximity to depressions are filled, and partial charge risk away from kitchen area. Most of the hydrocarbon are generated, expelled and accumulated between sedimentation of Lower Palembang Fm. to inversion time (10-5 Ma). The subsequent inversion is likely to have re-migrated hydrocarbon in Talangakar and Baturaja reservoirs along Benakat Gulley and associated fault bound folds.