Geomechanical Study Research Articles

Brittleness modeling of Cambay shale formation for shale gas exploration: a study from Ankleshwar area, Cambay Basin, India

Unconventional gas shales are described as organic-rich, fine-grained reservoirs and are typically dominated by clays. The shale gas reservoirs have received great attention in the past decade, because of their large reserves as well as recent technical advances in developing these resources. Accordingly, there are increasing demands to understand the petrophysical and mechanical properties of these gas shale rocks. The mineral composition and the presence of organic matter can influence not only the distribution of pores and fluid saturation, but also the effectiveness of stimulation. The geomechanical study of a shale gas reservoir is useful in identifying the intervals which can be fractured effectively. The estimation of geomechanical properties from well logs and their calibration with laboratory-derived properties on cores has been attempted in the present paper for Cambay shale of Cambay Basin, India, which is very much prospective for shale gas exploration. Powder X-ray diffraction (XRD) analysis was carried out on drill cutting samples in the study area, and it was seen that the major mineralogy is quartz, kaolinite, pyrite, calcite and mixed clays. Petrographic observation and Fourier transform infrared spectroscopy (FTIR) results also conform to the same minerals which are identified from XRD. Geomechanical properties (Young’s modulus, Poisson’s ratio, brittleness) of Cambay shale derived from sonic logs and density logs and are validated with the available predicted brittleness index (BI) from mineralogy through petrographic observation, XRD and FTIR interpretation results. Modeling using petrel software with log data and P-impedance was carried out and a relation between log results and P-impedance volume was established. The study concluded that (BI) varies from 0.44 (less brittle) to 0.75 (highly brittle) using both mineralogy and sonic logs. This study successfully identified the areas of high BI in the study area which can be an input for effective stimulation for shale gas exploration and exploitation.

Screening of Geomechanical Risks for Malaysian Development Field

Deeper drilling and exploitation of difficult reservoir is the new trend in oil and gas industry. Geomechanics study has, therefore, become a new requirement particularly for oil and gas field development. However, a complete geomechanics study is limited with the number of experts, time consuming and not a straightforward task. Therefore, there is an urgent need of a quick geomechanics screening criterion to be used as a standard guideline to evaluate the high level geomechanical risks and suitable analysis can be recommended for the identified development fields. The aim of this paper is to propose a screening criterion for geomechanical risks study based on four key parameters, drilling, depletion, injection and storage and sand production. The screening approach is designed based on Risk Assessment Matrix (RAM) risk screening where the likelihood is based on a set of scores developed to specific questions. The consequence for each failure scenarios is assessed based on educated estimation of the impact towards people, asset, environment and reputation. Recommendations for geomechanical study are made based on the severity of each failure category on the RAM risk matrix. Fourteen development fields in offshore Peninsular Malaysia, offshore Sarawak and offshore Sabah are selected for the assessment. Based on results, fields in offshore Sarawak and Sabah have higher potential for geomechacnical issues mainly because of their geological settings and formation characteristics. A set of geomechanical study is proposed for each individual field for prudent management of potential geomechanics risk associated with the depletion and EOR injection scheme planned for the fields.

Evaluation of the stability of a rock cliff by means of geophysical and geomechanical surveys in a cultural heritage site (south-eastern Sicily)

An integrated geophysical and geomechanical study is proposed for the evaluation of the fracturing condition and the stability of a rock cliff in the cultural heritage site of Ispica (southeastern Sicily).The site comprises several worship constructions such as the Friars Minor Monastery, the oldest construction of the village and a Church. The buildings stand on the edge of a 35 m high calcareous cliff, showing instability conditions related to the presence of deep fracturing and karst features. Due to possible future rockfalls the slope is expected to be subjected to retreat phenomena, which will threat the structures on top.The study of the seismic wave speed and of the environmental noise (microtremors), through active and passive seismic survey, proved useful in highlighting the spatial variation of the degree of fracturing in the rock mass. Moreover, the resonance frequency of the site allowed estimating the frequencies at which the ground motion is amplified by stratigraphic features.The stability analysis pointed out the critical condition of the slope, affected by different potential failure mechanisms with very low safety factors and a high probability of failure.All the considerations are contextualized in the wide Hyblean panorama, where important tectonic structures are responsible of the actual geological setting and of the seismicity of the area, as well as of the geomechanical condition of the slopes.

Unraveling chalk microtextural properties from indentation tests

The petrographical, petrophysical and geomechanical properties of the less commonly studied low permeability or tight chalks are presented in this study. The latter are relevant as potential unconventional reservoirs or intra-reservoir seals. Tight chalks encompass different lithotypes, in which the main factors controlling the petrophysical properties as shown in this study are the non-carbonate content and the degree of cementation. Those parameters strongly modify chalk microtexture and thus its porous network, reducing pore-sizes hence altering poroperm properties. In order to better understand the characteristics of tight chalks, an integrated petrographical, petrophysical and geomechanical study was carried out on a set of 65 chalk samples from Northwestern European outcrops, covering a wide range of lithotypes. The dataset gathered covers a broad spectrum of values for the determined petrophysical (e.g. porosities from 9 to 45%) and geomechanical properties (e.g. strengths from 3 to 60MPa). In the framework of this study, indentation tests were performed on the chalk samples. This technique proved to be a successful method to quickly estimate rock strength. Indeed, a good linear correlation (R2=0.90) has been established between indentation strength and UCS. Furthermore, indentation tests yielded valuable information about the chalk properties, both in terms of petrographical (cementation/clay-content), petrophysical (exponential relationship with porosity) and geomechanical (in relation to the elastic parameter and plasticity index) properties. This cheap and easy-to-operate method is a promising tool to indirectly estimate the mechanical parameters of chalks, when core samples are unavailable for laboratory testing in oil-field wells.

Integrated microseismic and geomechanical study in the Barnett Shale Formation

We have developed a careful chronological review of multistage stimulation treatments, in which microseismic interpretation was supported by fracture simulation and finite-element geomechanical simulation. The interpretation of a zipper frac stimulation treatment conducted in the Barnett Shale Formation in 2011 progressed from microseismic interpretation, from well-site observation, to a self-consistent understanding across multiple stages and multiple wells. Through this process, we have developed a tutorial on practical interpretation of microseismic data in the context of the hydraulic fracture treatment information (pump data) and regional structural information from interpretation of 3D seismic sections. Analysis of microseismic data included summarizing groups of events in the form of [Formula: see text]-value, [Formula: see text]-value, and extracted planar geometries. We advocate the development of a chronological interpretation, the consistency of which is tested using forward modeling. The process is iterative and relies on the forward modeling of complex fracturing and finite-element geomechanical models to inform iterations of the interpretation. Although extended case studies of this type are unsuitable for well-site analysis, we recommend their use for planning stimulation treatments for future nearby wells and to inform strategies for refracturing later in the well’s life.

Challenges to Geosteering and Completion Optimization of Horizontal Wells in the Cotton Valley Formation, East Texas

Summary Cotton Valley tight gas sands in the East Texas basin of North America consist of very-fine-grained, well-sorted quartz arenites and subarkoses that are overprinted by significant diagenetic processes. Stratigraphic variations in rock type control gas production. Hydraulic fracturing delivers economic gas production. We drilled horizontal wells more than 4,000 ft long consisting of more than 12 hydraulic-fracturing stages. The good gas-producing rock-type reservoirs are usually less than 14-ft thick and exhibit strong diagenetic overprint. Low gas prices challenge the use of sophisticated geosteering logs. By use of a very-basic gamma ray (GR) log and very-limited offset-pilot-well data, chasing such thin and variable sand bodies over a distance of 4,000 ft in a marginal marine sedimentary environment is daunting. Apart from this, horizontal wells that target thin layers present unique challenges to completion optimization. We acquired quad-combo log data, including azimuthal-density image data, by use of a logging-while-drilling (LWD) tool. We performed extensive log modeling by combining the horizontal well logs with logs from the two offset vertical wells, and achieved consistent interpretation. Log modeling has helped the post-drill well diagnosis in geosteering, completion design, and production performance. It has also supported formation evaluation. This study will highlight an integrated-study work flow in tight gas sands by use of openhole and cased-hole data. It will demonstrate the geosteering challenges, explain the log-modeling process, and display the formation-evaluation results. Geomechanical study, together with hydraulic-fracturing data and production-log data, will be used to confirm that good gas-producing rock types are easier to fracture, and they contribute better to production.

How to Approach Subsidence Evaluation for Marginal Fields: A Case History

This paper presents the evaluation of the subsidence potentially induced by underground storage of natural gas in a marginal depleted field located in Southern Italy. The critical aspect of the study was the lack of data because economic and logistic reasons had restricted data acquisition at the regional scale to perform a geomechanical study. This limitation was overcome by accurately gathering the available data from public sources so that the geometry of a largescale 3D model could be defined and the formations properly characterized for rock deformation analysis. Well logs, seismic data and subsidence surveys at the regional scale, available in open databases and in the technical literature, were integrated with the available geological and fluid-flow information at the reservoir scale. First of all, a 3D geological model, at the regional scale, incorporating the existing model of the reservoir was developed to describe the key features of a large subsurface volume while preserving the detail of the storage reservoir. Then, a regional geomechanical model was set up for coupled mechanic and fluid-flow analyses. The stress and strain evolution and the associated subsidence induced in the reservoir and surrounding formations by historical primary production as well as future gas storage activities were investigated. Eventually, the obtained results were validated against the measurements of ground surface movements available from the technical literature for the area of interest, thus corroborating the choice of the most critical geomechanical parameters and relevant deformation properties of the rocks affecting subsidence.

Paleostress inversion: A multi-parametric geomechanical evaluation of the Wallace–Bott assumptions

Wallace (1951) and Bott (1959) were the first to introduce the idea that the slip on each fault surface has the same direction and sense as the maximum shear stress resolved on that surface. However, this simplified hypothesis is questionable since fault mechanical interactions may induce slip reorientations. Earlier numerical geomechanical models confirmed that the slickenlines (slip vectors) are not necessarily parallel to the maximum resolved shear stress but are consistent with local stress perturbations. This leads us to ask as to what extent the Wallace and Bott simplifications are reliable as a basis hypothesis for stress inversion from fault slip data. Here, a geomechanical multi-parametric study using a 3D boundary element method, covering (i) fault geometries such as intersected faults or corrugated fault surfaces, (ii) the full range of Andersonian state of stress, (iii) fault friction, (iv) fault fluid pressure, (v) half space effect and (vi), rock properties, is performed in order to understand the effect of each parameter on the misfit angle between geomechanical slip vectors and the resolved shear stresses. It is shown that significant misfit angles can be found under specific configurations invalidating the Wallace and Bott assumptions, even though fault friction tends to minimize the misfit. We therefore conclude that in such cases, stress inversions based on fault slip data should be interpreted with care.

Geomechanical Aspects and Suitability of the Limestone (Sulaiy Limestone Formation) for Foundation Bedrock, Sulaiy Region, Saudi Arabia

The present study is a geomechanical study on the Sulaiy Limestone Formation Riyadh region, KSA which the limestone is the main rocks of the subsurface strata in this area. Due to high strength of rock formation, most of the buildings are designed on shallow foundations. Limestone strata may have cavities through its formation in some places which reduces the rock strength and increases its settlement. In our study, the geomechanical and physical analyses included point load strength (Is), uniaxial compressive strength (UCS), Schmidt hummer, dry density, porosity, permeability tests, (TCR), (SCR) and (RQD). The point load strength values are between 2.40 and 6.90 (Mpa). UCS of the different samples shows difference in values (55 to 143 MPa). Dry density shows slight differences in value (1.7 to 2.3 gm/cm3) with an average of 2.32 gm/cm3. Percentage of porosity is noticed by about (12%) and the lowest is (2%). The permeability is 22 milli Darcy (mD) (fair) and 202 milli Darcy (mD) (good). Schmidt hammer tests values are between 33 to 54. TCR is between 15-90%, SCR and RQD are between 20-90%. Then the allowable bearing stress is 18.90 kg/cm2. We can consider only 3.00 kg/cm2. The expected settlement is (Se=1.12 cm). Foundation level for building at 1.50 m below the lowest point on the ground surface. Finally, grouting should be added to fill the open cavities of limestone rock formation (if any) to the significant depth below footings before placing the foundations to gain more strength with reducing the limestone settlement.

Geomechanical modelling to assess fault integrity at the CO2CRC Otway Project, Australia

This paper presents the first published 3D geomechanical modelling study of the CO2CRC Otway Project, located in the state of Victoria, Australia. The results of this work contribute to one of the main objectives of the CO2CRC, which is to demonstrate the feasibility of CO2 storage in a depleted gas reservoir. With this aim in mind, a one-way coupled flow and geomechanics model is presented, with the capability of predicting changes to the in situ stress field caused by changes in reservoir pressure owing to CO2 production and injection. A parametric study investigating the pore pressures required to reactivate key, reservoir-bounding faults has been conducted, and the results from the numerical simulation and analytical analysis are compared. The numerical simulation indicates that the critical pore fluid pressure to cause fault reactivation is 1.15 times the original pressure as opposed to 1.5 times for the comparable analytical model. Possible reasons for the differences between the numerical and analytical models can be ascribed to the higher degree of complexity incorporated in the numerical model. Heterogeneity in terms of lateral variations of hydrological and mechanical parameters, effect of topography, presence of faults and interaction between cells are considered to be the main sources for the different estimation of critical pore pressure. The numerical model, which incorporates this greater complexity, is able then to better describe the state of stress that acts in the subsurface compared with a simple 1D analytical model. Moreover, the reactivation pressures depend mainly on the state of stress described; therefore we suggest that numerical models be performed when possible.

Prediction of seismic-wave velocities in rock at various confining pressures based on unconfined data

Laboratory measurement of P- and S-wave velocities ([Formula: see text] and [Formula: see text], respectively) under confining pressure indicates that with an increase in confining pressure, [Formula: see text] and [Formula: see text] will increase. The trend is exponential at low pressures, transitioning to linear above a critical pressure. However, the trend of the velocity-pressure curve for each rock specimen may be determined knowing the coefficients of this curve. We first studied how the coefficients of the velocity-pressure curve were expected to be functions of elastic moduli. Then, four empirical equations were used to estimate four coefficients of the velocity-pressure curve, using the rock density and [Formula: see text] and [Formula: see text] at atmospheric pressure (unconfined conditions). This analysis was carried out based on laboratory experiments on 285 rock specimens of different lithology from around the world, namely the United States, China, Germany, Iran, and deep-sea-drilling projects. For each rock specimen, [Formula: see text] and [Formula: see text] were measured at different confining stress levels, rendering more than 4000 data points. The accuracy of the estimated wave velocities was on the order of 2%–3% of the measured values on average. This methodology is especially valuable for prediction and analysis of the rock behavior at deep well conditions. This is applicable for predicting geophysical properties of the earth’s crust at depth, geomechanical study of hydrocarbon and geothermal reservoirs, wellbore stability analysis, and in situ stress determination.

The Mineral Character and Geomechanical Properties of the Transitional Rocks from the Mesozoic-Neogene Contact Zone in the Bełchatów Lignite Deposit

Beginning more than 30 years ago, opencast lignite mining in the "Bełchatów" area is an important source of accompanying minerals. Lignite mining in the "Bełchatów" mine yields, on average, more than 35 million tonnes per annum and requires removing more than 110 million cubic meters of overburden. Therefore the mine outside of the main mineral exploitation of lignite, leads to a large-scale economy of accompanying minerals. Part of the minerals are present in the overburden and are exposed on the slopes of the opencast mine; these minerals are selectively exploited in the event of the absence of recipients stored on anthropogenic deposits. The object of this mineralogical-geochemical study is a group of transitional rocks such as opoka-rocks, gaize and marls exposed when contact occurs between Neogene sediments and Mesozoic basement rocks in the "Bełchatów" lignite deposit. In the case of these rocks, during preliminary geological research carried out on the mine, doubt often appear as to their explicit petrographic character and hence their practical use. Advanced mineralogical methods allow mistakes in their identification to be avoided and a geomechanical study indicates possible direction of their practical use. The heterogeneous petrographic character of the examined rocks required the use of a broad research spectrum. The following microscopes were used in the framework of the mineralogical research: Polarizing Olimpus BX51 and electron (SEM) FEI Quanta 200FEG equipped with an X-ray spectrometer (EDX Genesis) and backscattered electron detector (BSE). In addition, observations were carried out using a cathodoluminescence apparatus, the Cambridge Image Technolgy Ltd CCL 8200 mk3 model, and a polarizing microscope, type Nikon Optiphot 2. Determination of the phase composition (qualitative and quantitative) was made using X-ray diffraction and utilizing the powder method of Debye-Sherrer. An X-ray diffractometer, a Philips PW 3020 X'PERT, was also used in the study. Analyses by Fourier transmission infrared spectroscopy were performed using the production apparatus BIO-RAD, model FTS 165, equipped with a package of programs for the digital processing of results. The chemical composition was determined by atomic absorption spectroscopy (AAS) using a spectrophotometer Philips PU 9100Xi Camera SX-100 and atomic emission spectroscopy with inductively coupled plasma (ICP AES) using spectrometer 40 PLASMA. The geomechanical properties were determined in accordance with the following standards: open and total porosity (PN-EN 1936:2001) compressive strength in air – dried state (PN-EN 1926:2001), bulk density and density (PN-EN 1936:2001), relative humidity (PN-EN 1925:2001); absorbability of stone material (PN-EN 13755:2002) and abrasion on the face of Boehme (PN-84/B-04111). Mineralogical-petrographic studies of the transitional rocks showed that the dominant component was SiO 2 which was presented in the form of opal type A and CT, chalcedony, quartz and microquartz. In addition, it was found that the rocks studied had been covered by secondary mineralization processes. The observations carried out showed that these rocks underwent primary silicification and decalcination processes, which contributed to the diverse petrographic nature of the rocks studied and secondarily experienced a change in their physico-mechanical properties. The silification process was the result of diagenetic processes taking place within the Neogene argillaceous rocks occurring when a sub-coal series is situated in the immediate vicinity of the bedrock. There was a release of extruded silica-rich water from the clays during the mechanical compaction process. Some amounts of silica may also be derived from plagioclase dissolution and the transformation of terrigenous material, mainly grains of potassium feldspar. The precipitation of silica from porous solutions occurred most when coinciding with the presence of carbonic acid formed by the decomposition of organic substances of vegetable origin. The studies carried out have a significant practical implication, as the transitional sediments from the "Bełchatów" lignite deposit can be used in the production of building materials. Against the background of a number of published papers on the rocks accompanying lignite seams there is a lack of the "Bełchatów" mineralogical-petrographic studies of the transitional sediments in the Mesozoic-Neogene contact zone in the "Bełchatów" lignite deposit taking into account the aspect of raw materials. This paper has been produced to fill the void in this area.

4D-3C geomechanical study of in-situ bitumen recovery in NW Canada using Toe-to-Heel Air Injection

Recent observations of shear-wave splitting in the near surface have been interpreted as a consequence of the stress state rather than the presence of fractures. The analysis of such shallow anisotropy measurements from shear-wave splitting on converted-wave data allows us to evaluate caprock integrity and detect areas where the stress in the caprock may deviate from the regional faulting regime. This information is vital in discerning whether the caprock is able to withstand recovery of shallow in-situ bitumen and heavy oil. Moreover, using time-lapse multi-component data, we can use the changes in split- ting azimuth and time delay to monitor overburden and reservoir changes occurring during production. Here we show that converted-wave splitting changes, observed at the Conklin Demonstration Project between 2008 and 2009, can be directly correlated to changes occurring in the overburden. Additionally, we show that the stress state of the overburden, and in particular the transition from one stress regime to another with depth, is considerably more complex than has generally been assumed.

勇払油ガス田におけるジオメカニクスによる生産性フラクチャーの評価

勇払油ガス田におけるジオメカニクスによる生産性フラクチャーの評価

Reservoir geomechanics for assessing containment in CO2 storage: A case study at Ketzin, Germany

Abstract This reservoir geomechanical study assesses the impact on top and fault seals integrity of fluid pressure changes associated with carbon dioxide (CO 2 ) storage in a saline formation. The case studied is the CO2SINK experiment at in Ketzin, Germany, where up to 60 ktons of CO 2 are being injected. Injection commenced in June 2008. A 3-dimensional (3D) geomechanical model of the site is built through integrated analyses of geologic, seismic, logging, drilling, and laboratory test data. First, the grid is expanded from a reservoir model up to surface, down to basement and laterally by about 3 times the pressure perturbation dimensions, while honouring all available structural, stratigraphic and lithological data. The grid cells are populated with density, poroelastic and strength properties upscaled from a 1-dimensional (1D) mechanical model built and validated along the Ktzi 201/2007 CO 2 injector well. Cells cut by faults are considered an equivalent medium representative of a jointed rock mass. The 3D geomechanical model is then dynamically linked to the reservoir model. Static equilibrium prior to injection is achieved by applying initial fluid pressure and gravity loads, as well as stress boundary conditions chosen so as to match in situ stress measurements. Stress path and rock deformation associated with CO 2 injection are then simulated. Pressure change data is passed from the flow simulator to the geomechanical simulator at selected time steps. Calculated stress path and strains are then used to investigate the possible occurrence and location of caprock failure and fault reactivation. Other results, such as ground surface elevation changes and sources of uncertainties are also highlighted. No failure is observed in the caprock and faults remain stable during CO 2 injection operations. Limited vertical displacement (maximum 5 mm) is predicted at surface.

Predicting Accelerating Subsidence Above the Highly Compacting Luconia Carbonate Reservoirs, Offshore Sarawak Malaysia

Summary Sarawak Shell Berhad has a number of offshore gas fields that produce from the Luconia carbonate formation, which can exhibit high-compressibility pore-collapse deformation. Recent accelerated subsidence has been observed at several of these fields, which extrapolates to final subsidence values well above previous estimates. This paper describes a geomechanical study involving core work to determine if the Luconia formation compressibility is sensitive to brine flow from the rising aquifer and a 3D geome-chanical finite-element model developed to predict future subsidence and lateral movements for the F23 platform. Compaction tests were performed on the Luconia core from three different gas fields. Tests on twin plugs were conducted—one plug undergoing a standard uniaxial zero-lateral-strain compaction test, while its twin has several pore volumes of simulated-formation brine flowed through it (at virgin in-situ stress conditions) before the compaction loading. Four sets of compaction tests on twin plugs were completed. The higher-porosity samples showed characteristic pore-collapse behavior consistent with previous measurements on Luconia mouldic limestone core. No sensitivity to brine flow was observed. In-situ compaction logs in the field also do not show increased compressibility in sections flooded by the rising gas-water contact (GWC). The geomechanical model uses a relatively simple structural model comprised of four layers—two overburden formations, the Luconia carbonate and one underburden formation. A nonlinear deformation model for the Luconia formation captures the accelerating pore-collapse response observed in the core and in-situ compaction measurements. The model is calibrated to GPS-measured platform subsidence and is consistent with measured core- and field-compaction properties. The results predict that platform subsidence rates with depletion would level off, with a maximum subsidence of 18.5 ft +/− 1 ft at an abandonment pressure of 300 psi. Platform subsidence in the two years following the work continues to follow the predicted values. This work illustrates the importance of integrated geomecha-nical core testing, field-monitoring measurements, and modeling to accurately predict compaction and subsidence effects in highly compacting environments.

Case Study: Geomechanics Enables Successful Horizontal-Well Drilling in Libya

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 111384, "Geomechanics Enables the Success of Horizontal-Well Drilling in Libya: A Case Study," by Kaibin Qiu, SPE, Schlumberger; Julio Gonzalez Felgueroso, Gabino Lalinde, Abdulmagid Naas, and Bernard Coste, Akakus Oil Operations; and John Fuller, SPE, Schlumberger, prepared for the 2008 IADC/SPE Drilling Conference, Orlando, Florida, 4-6 March. The paper has not been peer reviewed. Highly deviated or horizontal wells can incur instability problems. A case in Libya is presented in which significant difficulties were encountered during drilling of the first horizontal development well in a field in the Murzuq basin. The first two branches of the well were lost to severe instability problems. A comprehensive geomechanics study was carried out to determine the causes of the wellbore failure and to improve drilling design and drilling performance of additional development wells in the field. Introduction Horizontal wells can increase production rates and ultimate recovery and reduce the number of platforms or wells required to develop a reservoir. The geometry also helps to delay water or gas breakthrough, bypass environmentally sensitive areas, and reduce stimulation costs. In 2006, Akakus Oil Operations began drilling of the first horizontal development well, Well H1, in a field in Libya to avoid water coning and delay water breakthrough. However, unexpected drilling difficulties were encountered, and the first two branches of the well were lost. Before this project, many vertical exploration and development wells had been drilled in the same block without experiencing any major problem. A wellbore-stability study was carried out to determine the cause of wellbore failure in the horizontal well. A mechanical Earth model (MEM) was built for the analysis. The analysis identified the cause of wellbore instability as inadequate mud weight while drilling the overlying shale formation in the deviation-buildup section. The design of the second horizontal well was optimized on the basis of this study, and it was drilled without problems and ahead of drilling schedule. This case demonstrated that a comprehensive geomechanics analysis could improve drilling performance and reduce drilling costs. Data Audit Erroneous or inadequate input data impair wellbore-stability-analysis results, even in the most advanced analysis model. Therefore, a data audit is the critical first step. Relevant data for a geomechanical study were selected and gathered. Data included extensive information from different domains, such as daily drilling reports, master logs, wireline logs, geological data and reports, petrophysical interpretations, seismic data, and general field information. Those data were analyzed and cataloged, and data availability was identified. Redundancy of data and use of data from different sources and domains were highly desirable to achieve an internally consistent description of rock properties and stresses. Cross-checking and comparing data from alternative sources can highlight errors, inconsistencies, and omissions in the data that may need to be fixed or filled in at a later stage to improve the robustness of the predictions.

Geomechanical study for the exploitation of an underground marble quarry

The paper summarizes an essentially in-situ study for ground control at an Alpine underground white marble quarry. Rock material and rock mass structure have been characterized through laboratory tests and geo-structural exploration. The rock mass stress condition and a displacement monitoring was tested at a number of quarry locations. No evidence of appreciable deformation was experienced, but a high stress state was observed, showing the interaction effect between the mountain side and the underground excavations. Furthermore, a 2D and 3D BEM analysis is given for comparison.

Geomechanical study for the exploitation of an underground marble quarry

The Great Sphinx at Giza, Egypt was carved out of Middle Eocene limestone formations. They are highly porous and cavernous showing the evidence of having been greatly affected by water erosion. To investigate possible mechanism of its deterioration, the Japanese Sphinx Monitoring Mission organized by the authors carried out monitoring the monument site by means of moisture measurement, infrared thermal scanning, electric resistivity measurement, etc. in the winter of 1995. Also, the interaction between water and limestone was tested in the laboratory from the point of view on salinization and evapotranspiration. The daily cycle of moisture content and temperature at the Sphinx site has been clarified.

Relationships between pore pressure, stresses, and present-day geodynamics in the Scotian Shelf, offshore eastern Canada : N. A. Yassir & J. S. Bell, American Association of Petroleum Geologists Bulletin, 78(12), 1994, pp 1863–1880

A geomechanical study of the Mesozoic and Tertiary sediments beneath the Scotian Shelf shows that two major weak layers exist at depth: the overpressured unit at 4000 m and the basal Argo salt, which is ductile and diapiric. A consistent relationship is observed between the overpressures and the stress state in the basin. First, the smaller horizontal principal stress increases dramatically just above the onset of overpressuring, and secondly, borehole breakouts--indicators of stress anisotropy--decrease in abundance within the overpressured zone. Neither tectonic shear nor rapid burial can explain these observations; however, overpressuring by fluid generation will result in horizontal stress increase and eventually lead to an isotropic stress state. Compelling evidence is found for hydrocarbon generation being a key cause of overpressuring in the Scotian Shelf. Present-day horizontal stress orientations in the sediments overlying the overpressured zone are aligned with contours of equal overpressure, but not with the traces of Tertiary listric normal faults or with the shelf edge. This implies that contemporary stresses in these sediments are causally related to overpressuring. The upward transmission of lithospheric plate movements and associated stress is unlikely because the ductile Argo salt effectively detaches the sediments from basement. Instead, the rocks of the Scotian Shelf are attempting to slide down the geomechanically weak overpressured zone in the directions indicated by the breakouts, but they are prevented from doing so by the bowl-shaped basement structure in the region.