Al-Kandary, Ahmad (Kuwait Oil Company) | Al-Fares, Abdulaziz (Kuwait Oil Company) | Mulyono, Rinaldi (Kuwait Oil Company) | Ammar, Nada Mohammed (Kuwait Oil Company) | Al naeimi, Reem (Baker Hughes) | Hussain, Riyasat (Kuwait Oil Company) | Perumalla, Satya (Baker Hughes)
Role of geomechanics is becoming increasingly important with maturing of conventional reservoirs due to its implications in drilling, completion and production issues. Exploration and development of unconventional reservoirs involve maximizing the reservoir contact and hydraulic fracturing both of which are heavily dependent on geomechanical architecture of the reservoirs and thus require application of geomechanical concepts from the very beginning.
To support the unconventional exploration and conventional reservoir development in Kuwait, country-wide in-situ stress mapping exercise has been carried out in nine fields of Northern Kuwait. Stringent customized quality control measures were put in place to evaluate stress orientation. Cretaceous and sub-Gotnia Salt Jurassic rocks exhibit distinct patterns of stress orientations and magnitudes. While the variations in stress orientation in the Cretaceous rocks are within a small range (N40°E-N50°E) and consistent across major fault systems, the Jurassic formations exhibit high variability (N20°E-N90°E) with anomalous patterns across faults as well as in the vicinity of fracture corridors. Moreover, the overall stress magnitudes were found to be much higher in the strong Jurassic section compared with the relatively less strong Cretaceous strata. During the analysis, it was also observed that several natural fractures in Jurassic reservoirs appear to be critically stressed with evidences of rotation of breakouts.
Using geomechanical models from a specific field, the effects of in-situ stress, pore pressure and rock properties on formations were evaluated in inducing wellbore instability during drilling operations in a tight gas reservoir. It was found that the most favorable orientation for directional drilling is parallel to the maximum horizontal stress (SHmax) within that field.
The geomechanical study provided inputs not only for wellbore stability during drilling, but also regarding the response of natural fractures to in-situ stresses to become hydraulically conductive (permeable) to act as flow conduits. The fracture model of the field shows that the dominant fracture corridor trend in the field is NNE coinciding with present day in-situ maximum principal stress direction.
Vibrations are caused by bit and drill string interaction with formations under certain drilling conditions. They are affected by different parameters such as weight on bit, rotary speed, mud properties, BHA and bit design as well as by the mechanical properties of the formations. During the actual drilling process the bit interacts with different formation layers whereby each of those layers usually have different mechanical properties. Vibrations are also indirectly affected by the formations since weight on bit and rotary speed are usually optimized against changing formations (drilling optimization process). Therefore it can be concluded that for optimized drilling reduction of vibrations is one of the challenges.
A fully automated laboratory scale drilling rig, the CDC miniRig, has been used to conduct experimental tests. A three component vibration sensor sub attached to drill string records drill string vibrations and an additional sensor system records the drilling parameters. Uniform concrete cubes with different mechanical properties were built. Those cubes as well as a homogeneous sandstone cube were drilled with different ranges of weight on bit and bit rotary speed. The mechanical properties of all cubes were measured prior to the experiments. During all experiments, drilling parameters and the vibration data were recorded. Based on analyses of the data in the time and the frequency domain, linear and non-linear models were built. For this purpose the interrelations of sandstone and concrete mechanical properties, drilling parameters and vibration data were modeled by neural networks. Application of sophisticated attribute selection methods showed that vibration data in both, time- and frequency domain, have a major impact in modeling the rate of penetration.
The high-profile blowout at Macondo well in the US Gulf of Mexico, brought the challenges and the risks of drilling into high-pressure, high-temperature (HPHT) fields increasingly into focus. Technology, HSE, new standards, such as new API procedures, and educating the crew seem to be vital in developing HPHT resources. High-pressure high-temperature fields broadly exist in Gulf of Mexico, North Sea, South East Asia, Africa, China and Middle East. Almost a quarter of HPHT operations worldwide is expected to happen in American continent and the majority of that solely in North America. Oil major companies have identified key challenges in HPHT development and production, and service providers have offered insights regarding current or planned technologies to meet these challenges. Drilling into some shale plays such as Haynesville or deep formations and producing oil and gas at HPHT condition, have been crucially challenging. Therefore, companies are compelled to meet or exceed a vast array of environmental, health and safety standards.
This paper, as a simplified summary of the current status of HPHT global market, clarifies the existing technological gaps in the field of HPHT drilling, cementing and completion. It also contains the necessary knowledge that every engineer or geoscientist might need to know about high pressure high temperature wells. This study, not only reviews the reports from the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) and important case studies of HPHT operations around the globe but also compiles the technical solutions to better maneuver in the HPHT market. Finally, the HPHT related priorities of National Energy Technology Laboratories (NETL), operated by the US Department of Energy (DOE), and DeepStar, as a strong mix of large and mid-size operators are investigated.
Development of offshore hydrocarbon (HC) fields is today's oil and gasindustry priority in the Russian Federation. Water areas of the Arctic shelfare considered to be potential offshore HC production regions. When designingpipelines for such fields it is necessary to take into account the impact ofspecific Arctic conditions including hazardous ice impact (ice gouging),possible presence of permafrost on the seabed, lithological andgeomorphological distinctive features of bottom soils. All main parametersensuring safety of offshore pipelines must be determined and validated at theearly design stage.
The paper reviews one of the main conditions that influences reliable operationof underwater pipeline systems, namely, stable position of the underwaterpipeline at design reference marks.
Calculations of offshore pipeline stability on the seabed use the followingmain conditions:
- environmental conditions;
- geotechnical conditions of the seabed;
- bathymetrical conditions (water depth);
- pipeline parameters (diameter, wall thickness).
Criteria of pipeline stability on the seabed include:
Soils with weak strength properties, especially when they are used forbackfilling, may be potentially dangerous due to liquefaction underhydrodynamic forces. It is especially dangerous in the first years of operationwhen the soil is not consolidated enough. Relief in a local zone of dilutedsoil causes longitudinal stresses in pipeline, which may result in offshorepipeline stability loss. Liquefied soil potential depends also on backfillingprocess technology. This operation is performed by special ships - dredgers.Such ship has two pipes, one for soil suction, and the other equipped withwater injection nozzles - for washing out and backfilling. When a trench isbackfilled with controlled soil flow, "front" of backfill material is formedunder pipe working head and a layer of fluidized material appears in the upperpart of this "front". Therefore, if weak soil is used as backfill material, asize of liquefied soil layer will be considerable, as well as its impact on thepipeline. This process may lead either to floating up or submerging of pipelineinto the soil. To stabilize offshore pipelines position the following measurescan be taken: backfilling with soil not subject to liquefaction; pipelinelaying below the layer of liquefied soil to eliminate risks related to soilliquefaction; using different methods of ballasting.
A two-year-long field study was conducted by ConocoPhillips Alaska, Inc. andPND Engineers, Inc., at Kuparuk in Alaska's arctic North Slope region. Thestudy verified that pipe piles can be directly driven into predrilled pilotholes in frozen ground, without requiring thermal modification of thepermafrost. The traditional "drill-and-slurry" method of permafrost pileinstallation involves hanging piles in an oversize hole and backfilling theannulus with a sand/water slurry. Vibratory driven pile installation isconsiderably more efficient with large benefits in installation time, expenses,and safety. Both methods require an adequate adfreeze bond for pileperformance. The objective of this testing program was to determine whetherdespite great benefits in installation efficiency the vibratory driven pilewould perform adequately. Twelve 12.75-inch-diameter steel pipe piles wereinstalled in permafrost in the Alaskan arctic; eight piles were installed inice-rich sandy silt and four piles were installed in a frozen gravel soil.Piles were loaded in tension for six different durations ranging from five daysto six months at loads varying from 35 kips to 145 kips. At the completion oflong-term testing, the test piles were unloaded, rested, and then loaded tofailure to characterize the adfreeze short-term strength. Pile load anddisplacement were continuously recorded with electronic displacement and loadtransducers. Subsurface soil temperatures were also monitored. Collected datawas used to characterize long- and short-term pile velocity as a function ofload and adfreeze temperature. Experimental results were compared to currenttheoretical and empirical performance.
Pipeline systems are integral components of the system infrastructure forthe transport of hydrocarbon resources. In arctic and harsh environments, thesepipelines may be subject to large deformation geohazards. Pipeline/soilinteraction events are often examined using a structural pipe/spring model.This approach does not account for more realistic soil constitutive behaviour,soil deformation mechanisms and effects of soil load transfer on pipelinemechanical response. This paper examines pipe/soil interaction events duringoblique lateral-vertical soil movements using plane strain finite elementanalysis. The results from this study provide a technical framework to assessthe effects of geotechnical loads on buried pipelines, highlight key parametersinfluencing soil yield envelopes, and identify soil failure mechanisms foroblique pipe/soil interaction events that can be used in the design of buriedpipelines for large deformation geohazards. The results may be used tobenchmark more complex loading events, such as coupled ice keel/seabed/pipelineinteraction, that has limited physical basis for validation.
The five Arctic regions of Russia, Alaska, Norway, Greenland and Canada holda tremendous potential for both discovered and undiscovered reserves of Oil andGas. The USGS estimates 160 BBO, and 1,670 TCF of natural gas reserves in theArctic, with most of these reserves being located offshore. The Arctic region,however, presents its own unique challenges; extreme low surface temperatures,a highly fragile environment protected by strict regulatory controls, very highcost of operations - and of failure prevention, and a narrow weather window tooperate. Combined, these challenges leave no room for complacency whileplanning an Arctic drilling campaign. The drilling tubular risks are mainlyaccentuated during transportation, storage, and surface handling in thepermafrost region. In order to drill safely and reliably in such harsh surfaceconditions, ordinary drillstring solution is neither considered safe norreliable due to the adverse and unpredictable effect of extereme lowtemperatures on mechanical properties of steel. VAM Drilling has successfullydeveloped and deployed proprietary Arctic steel grades that deliver a greatcombination of strength and ductilitly at temperatures as low as -60°C(-76°F).
In predicting the geotechnical constraint against pipeline movement usingfinite element methods, the treatment of the pipe/soil interface contactbehavior is of utmost importance, especially in the tangential direction. Thisstudy focuses on the interpretation of soil resistance to axial pipe movementin cohesive soil material for oblique loading, specifically the effect ofchanging the interface shear stress limit and friction coefficient. The mainfinding of the present study is that the incorporation of a shear stress limitin the definition of tangential shear behavior has a considerable effect on theaxial pipeline reaction forces. Without the shear stress limit, the maximumaxial forces due to oblique pipe movement are effectively doubled in comparisonto a limit equal to half of the undrained shear strength. A simple analyticalmethod is provided to estimate the maximum oblique axial soil resistance inundrained conditions. The effect of changing the assumed frictional behavior isalso discussed with respect to predicting the soil reaction forces acting on anice keel during an undrained gouging event in cohesive soil.
Lee, Yun-Hee (Korea Research Institute of Standards and Science) | Kim, Yongil (Korea Research Institute of Standards and Science) | Park, Jong Seo (Korea Research Institute of Standards and Science) | Nahm, Seung Hoon (Korea Research Institute of Standards and Science) | Yoon, Ki-Bong (Chungang University)
In order to estimate the hardness and yield strength of an indented material, advanced methods have been developed for extracting closed boundaries of the contact area and the plastically deformed zone from 3D nanocontact morphologies. However, this image processing technique cannot be applied to shallow indentations as it results in weak surface pile-ups. Based on the modified volumetric approach, the new hardness and yield strength of Au film and fused quartz are compared with those from the indentation curve analysis and differential contact analysis.
Nanoindentation measuring applied load and indenter penetration depth during a contact deformation is one of the most powerful techniques for evaluating the mechanical properties of small volume materials (Oliver and Pharr, 1992). Typical nanoindentation researches have been constrained within the determination of elastic modulus and hardness. However, the research scope is now being expanded to the analysis of plastic flow curve, yield strength, residual stress, fracture toughness, interfacial adhesion and various tribological properties (Ahn and Kwon, 2001; Lee et al., 2006; Lee and Kwon, 2002; Lee and Kwon, 1999). However, since the deformation morphology under indentation loads less than mN cannot be easily observed, 2 models have been developed (Oliver and Pharr, 1992; Doerner and Nix, 1986) for characterizing Ac at the peak indentation load from the nanoindentation curve. The method commonly used for analyzing the nanoindentation load-depth curve is that proposed by Oliver and Pharr (1992), expanding on an earlier work by Doerner and Nix (1986). Below, the analyzed data based on the Oliver and Pharr method will be denoted as O&P. However, the O&P method (Oliver and Pharr, 1992) can strongly underestimate the contact area if a material pile-up is involved, as reported in the finite element simulation work of Bolshakov and Pharr (1998).
Li, Yanghui (Dalian University of Technology) | Song, Yongchen (Dalian University of Technology) | Liu, Weiguo (Dalian University of Technology) | Yu, Feng (Dalian University of Technology) | Wang, Rui (Dalian University of Technology) | Nie, Xiongfei (Dalian University of Technology)
To acquire more knowledge about the mechanical properties of gas hydrate-bearing sediments and assess the longterm stability of the strata, samples of clayey sediments containing methane hydrate were prepared and tested for their mechanical properties under various conditions by triaxial compression. The effects of temperature and confining pressure on the mechanical properties of methane hydrate-bearing sediments were analyzed. And a strength criterion considering the influence of temperature was developed for methane hydrate-bearing sediments. It agrees well with the experimental data, it and can be taken to predict the shear failure strength of methane hydrate-bearing sediments under subzero conditions.
Gas hydrate has attracted global attention due to its widespread occurrences and large potential as an energy resource (Brown et al., 2006; Glasby, 2003). It generally exists in the regions of Arctic permafrost and submarine continental margins where there are acceptable P/T conditions (MacDonald et al., 1994). Additionally, the naturally occurring hydrates are always associated with large quantities of gas trapped underneath, with the hydratebearing strata acting as seals for trapped free gases. Gas may release abruptly during mining and well drilling, which can lead to blowouts and well-control problems (Cameron et al., 1990; Vanoudheusden et al., 2004). Characterizing the mechanical properties of gas hydrate-bearing sediments will provide a scientific basis for the evaluation of the safety of the structure and the stability of the reservoir. Up to now, the mechanical properties of gas hydrate-bearing sediments have not been fully understood. Durham et al. (2003) and Stern et al. (1996) indicated that the mechanical properties of methane hydrate are very different from those of water ice. Winters et al. (2004, 2007) studied the strength and acoustic properties of laboratory-formed methane gas hydrate. However, the analyses of the mechanical properties of gas hydrate-bearing sediments under various conditions are qualitative.