Reddy, S. S. (Oil and Natural Gas Ltd) | Anjaneyulu, J. V. (Oil and Natural Gas Ltd) | Lal, Abhay Kumar (Oil and Natural Gas Ltd) | Rao, E. J. (Oil and Natural Gas Ltd) | C H, Ramakrishna (Oil and Natural Gas Ltd) | Talreja, Rahul (Schlumberger) | Bahuguna, Somesh (Schlumberger) | Zacharia, Joseph (Schlumberger) | Chatterjee, Chandreyi (Schlumberger) | Basu, Jayanta (Schlumberger)
Malleswaram field in Krishna-Godavari (KG) basin has proven gas reserves in the late Cretaceous Nandigama formation. Many drilling challenges were faced, including losses, tight hole, and stuck pipe in the Raghavapuram and Nandigama formations overlying the reservoir interval. This study was conducted to provide a solution for drilling optimization by mitigating drilling-related nonproductive time (NPT). Integration of acoustic and geochemical data for geomechanics study provided a new insight into cause of overpressure and need for revamping of casing policy to significantly improve wellbore stability, mitigate risks, and ensure future drilling success. Generated stress models can be used to optimize hydraulic fracturing in these reservoirs. A completion quality based on stress model indicates the need for multistage fracturing due to the presence of stress barriers inside sand units in Nandigama formation.
Augustine, M. (Oil and Natural Gas Ltd) | Murthy, A. V. R. (Oil and Natural Gas Ltd) | Boindala, Amitha (Oil and Natural Gas Ltd) | Bahuguna, Somesh (Schlumberger) | Talreja, Rahul (Schlumberger) | Pattanaik, Sambit (Schlumberger) | Kalita, Deepika (Schlumberger) | Das, Sourav (Schlumberger)
Madanam field in Cauvery basin in the east coast of India, has fractured gneissic basement. As exploration focus moved to unconventional reservoirs, the gneissic basement of Madanam was seen as a potential reservoir. However, ambiguity existed about the fluid flow through the basement. For example, in Madanam field, one well (well A) flowed whereas another well (well B) located 8.5 km away had minor flow from the basement reservoir that lasted 2 days. The main purpose of this study was to find possible reasons for this anomalous behavior. This study was conducted by integrating sonic and image measurements with a geomechanics workflow to identify critically stressed open fractures. Further, this work aims to provide a fit-for-purpose solution to optimize and prioritize testing zone selection in near real time.
Alkamil, Ethar H. K. (University of Basrah, Missouri University of Science and Technology) | Abbood, Husam R. (Missouri University of Science and Technology) | Flori, Ralph E. (Missouri University of Science and Technology) | Eckert, Andreas (Missouri University of Science and Technology)
During drilling operations for the E oilfield in the Mishrif formation in southern Iraq, stuck pipe has been identified as a significant geomechanical problem for several wells. In this study, a 1-D mechanical earth model (MEM) of the Mishrif formation is compiled based on its state of stress and rock strength parameters and is utilized to assess the contribution of borehole collapse leading to the stuck pipe problems.
The MEM model is based on the principal in situ stresses and their orientation obtained from wireline logs measurements, measuring while drilling (MWD), and leak off test (LOT). Rock strength properties are obtained from empirical equations and extended leak off tests. The in situ stresses are transformed to calculate and analyze mud pressure conditions for all wellbore azimuths and inclinations. Two different failure criteria (the Mohr-Coulomb and Mogi-Coulomb rock failure criteria) are used in order to determine feasible drilling trajectories (with respect to the σH orientation) and mud pressure conditions for several wells.
This work was conducted to study the behavior of the collapse pressure for Mishrif formation under a normal faulting (NF) in situ stress regime. The results of this study show that wells characterized by stuck pipe are drilled along azimuths which promote wellbore collapse. Based on the MEM results, the mud pressure window is calculated, and stable azimuths and inclinations for each well are suggested. If a specific azimuth for a well cannot be altered, an optimum inclination is recommended to reduce the severity of the borehole collapse. This study based on a 1-D MEM model for directional drilling can improve the well drilling efficiency by reducing non-productive time due to the wellbore instability.
ABSTRACT: The failure mechanism of haulage gate surrounding rock in 402103 fully-mechanized top-coal caving face of some deep coal mines of Bin-Chang Mining Region in Shan-xi province are studied. The results show that haulage gate surrounding rock in deep coal mine has the characteristics of big deformation, asymmetry stress distribution of surrounding rock complex. Based on the support idea, which is first pressure released, second pressure relief, third anti-pressure, support and on-site monitoring program for haulage gate in 402103 fully-mechanized top-coal caving face is carried out. The practice shows that the design support parameters of crossheading are reasonable, and the supporting effect meets the needs of safety production.
With the increase of the mining depth, geological environment becomes more complex; the roadway surrounding rock shows characteristics of large deformation, high stress and sustainable creep, and the risk of roadway rock burst has been increased greatly. At the same time, deep roadway is influenced by high temperature, high confining pressure and high pore pressures; Deformation of the surrounding rock in roadway shows new characteristics that are different from shallow tunnel.
Domestic and international scholars have conducted extensive research on the issue of deep roadway support (He et al. 2007, Kang et al. 2010, N. Zhang et al. 2009, Bai et al. 2007). But the research on the issue of roadway support in special thickness coal of deeply buried coal mine was relatively less.
In order to ensure the safety of construction, the research on the issue of roadway support in special thickness coal of deep buried coal mine is necessitated; we should put forward reasonable and feasible supporting solutions, and provides a reference for other roadway support of deep buried coal mines in the west. Take the support problem in concern, a support scheme is proposed and engineering practice and deformation monitoring are carried out.
Lian, C. J. (Shandong University of Science and Technology) | Hou, J. Z. (Shandong University of Science and Technology) | Gao, G. L. (Taian Taishuo Strata Control Science and Technology Co. Ltd.) | Wang, G. (Taian Taishuo Strata Control Science and Technology Co. Ltd.) | Song, W. T. (Henan Polytechnic University)
ABSTRACT: It has wide distributions and large recoverable reserves of Jurassic period coal seam in China. It is difficult to maintain stability of the development roadways with long service term for Jurassic strata because there are abundant argillaceous rocks and some minerals in the high argillaceous rocks will be expanding while meeting with water. The fractures of the roadways develop well under high stress and are suitable to filling with grouting. But the poor cementing performance of cement with argillaceous rock as well as a heavy water filtration rate of cement slurry had resulted in failures of many engineering cases adopting cement grouting to reinforce this kind of roadways. In this paper, according to characters of the high argillaceous rock in Jurassic strata, a marlaceous inorganic grouting material which possesses the well cementing performance with argillaceous rocks and little filtration rate was introduced; and the grouting reinforcement mechanism, construction technique and engineering application effect about it was clarified. It will be of great significance for reinforcement and maintenance of the development roadways with high argillaceous rocks.
According to statistics, 60% of the proved coal reserves in China distributes in Early-Middle Jurassic period of northern North China, southern Northeast China and Northwest China, along with late Jurassic to early Cretaceous period of Northeast China and east Inner Mongolia. The period of coal forming is short and argillaceous rocks are abundant in Jurassic strata. Moreover, there are quite a few expanded minerals in some strata. So the roadways are easily to be deformed and damaged when affected by mining-induced stress. In addition, this kind of soft rock roadways has an obvious time effect. For the development roadways with long service term, serious deformations are frequently observed and part of the roadways has suffered deformation and maintenance time after time. The stability support of the development roadways really need much cost.
ABSTRACT: The vertical stress, failure patterns and deformation of roadway surrounding rock under different coal pillar width are studied by using FLAC3D software. The results show that with the increase in the width of coal pillar, stress concentration range and factor in pillar decreases, gradually showed uniform bearing form, at the same time, the displacement of roadway and plastic zones in pillar gradually decrease. With the increase of the width of coal pillar, the range of elastic core is larger, indicating that the more stable the roadway coal pillar is, the more safety will be. Taking into account that large coal pillar width would result in the waste of resources, the reasonable coal pillar width is between 14-16 m.
According to numerous studies on the rational section coal pillar, many effective methods to determine the reasonable size of coal pillars can be categorized as follows (Cui et al. 2012, Tu et al. 2011, Zhang & Shi 2004, Chen 2014, Shao et al. 2014): 1) Mathematical statistics, a large number of measured results give rise to inductive reasoning that unstable surrounding rock conditions of coal pillar size; 2) Application of mine pressure regularity with various coal pillar and empirical formula to analyze the reasonable size of the coal pillar; 3) The reasonable coal pillar width range determined based on measured pillar abutment pressure distribution method analysis of coal seam; 4) According to the limit equilibrium theory to derive the coal hold steady when the width formula; 5) The estimation formula of three dimensional plastic zone width of coal pillar stress. The numerical simulation of roadway surrounding rock is performed to analyze the width of coal pillar under different stress and movement for working face 222203 in Shuangxin Mining Co. coal mine, Inner Mongolia.
ABSTRACT: Inverse analysis is commonly used in identifying geomechanical parameters based on the monitored information such as displacement or stress. Conventional inverse analysis method is incapable of recognizing non-linear relationship involving displacement, stress and mechanical parameters effectively. A hybrid model which combined Multi-output-Support Vector Machine (MSVM), Artificial Bee Colony (ABC) and numerical analysis has been proposed to estimate the in situ stress and rock mechanical parameters based on borehole fluid pressure. MSVM is used to represent the non-linear relationship between parameters of numerical model and borehole fluid pressure. ABC is used to search the set of unknown recognized parameters based on the objective function. Numerical analysis of hydraulic fracturing is used to create the necessary training and testing samples for the hybrid MSVM-ABC model. Results of numerical experiments demonstrate that a hybrid MSVM-ABC model for inverse analysis can effectively identify in situ stress and rock mechanical parameters based on wellbore fluid pressure in the hydraulic fracturing process.
Geomechanical parameters such as Young's modulus and in situ stress in the field of petroleum are important to reservoir simulation, borehole stability analysis and production of petroleum (Gokceoglu et al. 2004, Juliusson 2012). However, it is difficult to obtain those parameters accurately and efficiently using the traditional laboratory test and in-situ test because of the complex, nonlinear and uncertainty of rock mass characters (Zhao & Yin 2009). Inverse analysis method provides a good way to get these parameters by combining the field-observed information with numerical simulation. Inverse analysis are commonly used in rock mechanics and engineering such as tunnel, underground engineering and rock slope etc (Sakurai & Takeuchi 1983, Gioda & Maier 1980, Miranda et al. 2011, Feng & Hudson 2011).
In the petroleum industry, hydraulic fracturing is the most common technique to perform well stimulation and earth stress characterization of hydrocarbon reservoirs, especially for unconventional reservoirs such as shale gas, tight gas and coal bed methane. In this paper, geomechanical parameters were estimated by combining inverse analysis and hydraulic fracturing test.
In this paper the authors report the vertical bending properties of a test chilled gas pipeline and the countermeasures of the bending. A full-scale field experiment of the chilled gas pipeline system was conducted in Fairbanks, Alaska from 1999 to 2005. The length of the test pipeline was 105m and the diameter was 0.9m. The circulated chilled air was –10°C. One-third of the pipeline was buried in frozen ground and the rest of it was placed in talik. At the end of July 2003, circulation of the chilled air ceased, however, monitoring of the thaw settlement-related properties of the test pipeline continued until the middle of April 2005. The following results were presented at the 2nd ATC: 1) As the frost-bulb around the pipeline in talik section formed, the test pipeline in the talik section moved upward, resulting in bending of the pipeline at the boundary. 2) In summers, frozen overburden soil of the pipeline became thinner due to thawing of active layer above. The pipeline buried in frozen section moved upward abruptly, fracturing the thinning frozen overburden ground. 3) The phenomenon mentioned in 2) occurred in successive summers, and the pipeline uplift in frozensection continued. 4) In relation with 1), the upward movement in talik section was confirmed by frost heaving of the pipe foundation. In this report the bending behavior of the test pipeline is described and the several methods to deal with the bending are proposed.
This paper presents a significant methodology advancement that addresses one of the industry's most challenging problems: the accurate prediction of detailed local stresses in unbonded flexible risers. Flexible risers exhibit highly nonlinear dynamic behavior due to the stick/slip interaction between the pipe wall layers in compliant systems that undergo large three-dimensional translations/rotations. Practical, accurate prediction of critical flexible pipe component responses requires an efficient method capable of incorporating detailed flexible pipe models into a global nonlinear dynamic analysis. Current industry practice is a two-step global/local approach involving a global nonlinear analysis with 1D centerline models, which may include bending hysteresis effects, followed by local analysis of a detailed model segment to the global results to predict critical response items such as armour wire stresses.
A Nonlinear Dynamic Substructuring (NDS) framework is developed that expands the classical methods of dynamic substructuring and component-mode synthesis to geometrically and locally nonlinear problems. This evolution/integration of capabilities enables the computationally efficient inclusion of detailed flexible pipe models into, and recovery of detailed response/stress time-histories directly from, the global nonlinear analysis itself. The NDS methodology is benchmarked against published work involving the large deformations static and dynamic global analysis of a flexible riser. The full potential of the method is then demonstrated by efficiently incorporating 3D detailed flexible pipe substructure models, with bending hysteresis, into a global system nonlinear analysis and recovering stress time-histories in tensile armour layers.
The accurate prediction of local stresses in flexible risers has been an industry objective for some time. Flexible pipe has a complex structure composed of multiple interacting pipe wall layers (Figure 1). The stick/slip friction hysteretic behavior of these layers is directly coupled to the global large displacements of the overall compliant system resulting in a highly nonlinear problem. A common approach for analyzing flexible risers is to conduct the global analysis with standard line elements utilizing the flexible pipe's unpressurized linear bending stiffness.
Steel Catenary Risers (SCR) and hybrid riser towers have been an attractive choice for recent deep-water field developments. However, design of SCRs for harsh environments or from large motion host platforms remains a significant challenge. The key issues for the design of SCRs in harsh environments are the fatigue near the hang-off and at the touchdown point. Hybrid riser towers have their own challenges and need special bottom assemblies with heavy foundation and complicated spools.
A new un-coupled riser concept is presented called the Catenary Offset Buoyant Riser Assembly (COBRA). COBRA consists of a catenary riser section with a long, slender buoyancy module on top which is tethered down to the sea bed. The top of the catenary riser section is connected to the host platform by a flexible jumper. COBRA is an efficient riser arrangement for host platforms with large motions, e.g. FPSO or Semi submersibles. The flexible jumpers in this riser system effectively absorbs the platform motions, and consequently the steel catenary riser section has almost no dynamic motions, which improves both strength and fatigue performance.
The riser system is developed for water depths ranging from 750 m to 3000 m in harsh Northern Norwegian environments. The results clearly indicate that it is possible to have a robust design of COBRA risers from large motion host platforms in harsh environments using presently qualified material and technology. The first order wave fatigue response of the steel riser section is negligible and the fatigue is purely controlled by VIV and can be mitigated by the use of VIV strakes. The preliminary work also showed that this riser system can easily be installed in harsh environments. The riser components used in this riser system are all field proven as they are used in other riser systems.
This concept is also applicable in less demanding environments, such as in Brazil. Furthermore, due to reduced dynamics in the SCR part of the risers, cost effective CRA materials like mechanically lined pipes can be used in the SCR section, thereby reducing the costs considerably.
The COBRA riser concept will make the applicability of catenary risers a credible alternative option for use in increasingly harsh environments or from host platforms with large motions. Since the components in this riser system are all fully qualified material they are cost effective and ready for project application.