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Abstract The integration of core based rock mechanics with the open hole log and seismic geophysics technologies, has created added value through operational costs savings for Chevron's world-wide drilling and completion holdings. Early development of this integrated technology focused on supplementing core measured rock property data with open hole log measurements to obtain rock mechanical property estimates throughout the horehole. Log derived mechanical property estimates have lead to the development and worldwide use of the following applications:formation drillability assessment for bit optimization and performance prediction, wellbore stability for extended reach and horizontal wells, sanding predictions for completion design, and formation stress profiling and elastic properties modeling for hydraulic stimulation design. The characterization of rock mechanical properties, in the absence of core, hinges upon the newly created capability of predicting formation shear wave propagation velocities. This breakthrough technique was first developed to estimate formation shear wave velocities for single well (1D) mechanical property predictions using conventional open hole measurements- (compressional wave velocity and bulk density). The technique was then enhanced to utilize surface seismic data sets in a 1D sense to predict formation mechanical properties at undrilled prospect locations. The links to the seismic world have proven particularly valuable for rank wildcat and step out drilling applications where offset well control is absent or extremely limited. The latest innovation has been to characterize volumetric (3D) formation mechanical properties from 3D seismic data cubes. Volumetric rock properties currently determined include Poisson's ratio, horizontal stress magnitude, borehole breakdown pressure gradient, pore pressure gradient and unconfined compressive strength. This paper summarizes the shear wave velocity estimation technique and presents several examples. Field examples will also be shown that demonstrate successful applications of log derived mechanical properties for rock strength and minimum horizontal stress profiling applications for fracture stimulation design. A full set of volumetric formation mechanical property cubes will then be presented, demonstrating the feasibility of using 3D seismic data for well planning. P. 241
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (0.96)
- Geophysics > Seismic Surveying > Seismic Modeling (0.70)
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Abstract Stress trajectories around faults have been simulated with a 3-D finite element model, based on 8-model brick elements in five layers. Preliminary simulations imply that stress trajectory deflections in the neighbourhood of fault zones can be expected if there is a large geomechanical contrast between the fault zone and the adjacent rocks and if far field stress anisotropy is small. On the other hand, if the horizontal stress anisotropy is large, significant stress deflections appear unlikely to occur near a fault. Within a softer' fault zone H will be aligned approximately parallel to the trend. Magnitudes of maximum and minimum stress are modelled for soft and hard fault simulations. Significant modifications in stress magnitudes developed in the vicinity of the fault zones. P. 33
- Europe (0.95)
- North America > United States > Oklahoma (0.46)
- Geology > Structural Geology > Fault (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Europe > United Kingdom > North Sea > Central North Sea > Moray Firth > Moray Firth Basin > Witch Ground Graben > Block 15/22 > Scott Field (0.99)
- Europe > United Kingdom > North Sea > Central North Sea > Moray Firth > Moray Firth Basin > Witch Ground Graben > Block 15/21a > Scott Field (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 375 > Block 34/7 > Snorre Field > Statfjord Group (0.98)
- (11 more...)
Abstract This paper presents relationships for estimating horizontal stresses based on the assumptions that the in situ stress state in a petroleum basin is controlled by the bounding normal or thrust faults at a limit equilibrium and that the fault block is linear elastic and plane strain condition applies in the direction parallel to the strike of the fault. These relationships are an extension of an earlier study and include the effect of residual friction angles on the estimation of horizontal stresses at depth. The result shows that re-orientation of the minimum principal stress is possible after faulting depending on the Poisson's ratio of the formation. Predictions based on the relationships are compared with the stress data obtained in normal and thrust fault conditions as well as with the change in the minimum horizontal stress induced by the pore pressure depletion. The results show that to match the field stress data, a relatively low residual friction angle (100 โ 300) on the fault is required. This is further supported by the numerical modelling of the in situ stresses in the Cusiana field in Colombia, and is consistent with the residual friction angles measured in laboratory or back-calculated based on earthquake mechanism. P. 59
- North America > United States > Texas (1.00)
- North America > Canada (1.00)
- South America (0.69)
- Europe > Norway (0.68)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.69)
- Geology > Structural Geology > Fault > Dip-Slip Fault > Reverse Fault > Thrust Fault (0.56)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.47)
- South America > Colombia > Casanare Department > Llanos Basin > Cusiana Field > Mirador Formation (0.99)
- North America > United States > Texas > Travis Peak Formation (0.99)
- North America > United States > Texas > East Texas Salt Basin (0.99)
- (7 more...)
Abstract Observations of triaxial creep and stress relaxation of unconsolidated reservoir sands imply markedly different static and dynamic modulii and may explain observations of very low differential stresses found in the Wilmington Field, CA, the Gulf of Mexico, and elsewhere. Triaxial testing performed on 1 inch plugs of reservoir sands under both stress- and strain-controlled conditions show transient stresses and strains. All tests were performed under dry or drained conditions to eliminate poroelastic effects. We previously observed creep under hydrostatic stress conditions in these unconsolidated sands. The resulting strain vs. time curves could be fit with a standard linear solid viscoelastic model that had a relaxation time of about 10 hours. The data demonstrates the rock's ability to dissipate stress through relaxation and creep. The reservoir material shows viscoelastic rheological behavior in both creep and relaxation tests which appears to be related to the presence of intergranular clay. Measurements of the static Poisson's ratio under large strains yielded values .29 which suggests that the particles in the matrix efficiently coupled the principle strains. P. 465
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.94)
Abstract This paper describes, for the first time, a unique investigation of ASR using synthetic sandstone samples formed under applied polyaxial stresses. The strain relaxation in all tests invariably gave a good indication of the principal stress orientations. Measured strain relaxation ratios were approximately equal to corresponding applied stress ratios up 1.5, suggesting that, with a knowledge of one of the principal stresses, in regions of low stress anisotropy, stress can be calculated directly from strain. At stress ratios of 2 and above, corresponding relaxation strain ratios were variable, time- dependent and generally higher than the stress ratios. This suggests that shear stresses associated with stress anisotropy result in material damage that is partly responsible for the measured relaxation strain. Correction of strains for "Poisson" effects reduced data scatter at the higher stress anisotropies but gave a poor correlation between applied stress and a) strain magnitudes, b) calculated stress, for a measured Poisson ratio (v) of 0.3. Lower v values gave better data fit, but it is suggested that the use of a Poisson correction of (he measured strain. Using low values of v, is unrealistic. The strain relaxation mode was assessed using the Kelvin-Voight model. The strain relaxation curves are not perfectly linear in normalised strain/time space. The material behaviour cannot therefore be fully reproduced using this visco-elastic model. Anisotropic samples especially seem to deviate from a linear trend, again suggesting that stress anisotropy and related fabric damage have an effect on the ASR response. P. 161
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.64)
Abstract The selection of horizontal wells as barefoot and multilateral well candidates requires consideration of the well integrity over the producing life of the field. The evaluation of the production lifetime of a well requires that both the mechanical and chemical changes which the well experiences be modeled and predicted during the well design. The mechanical changes which the well will experience during production is primarily a function of stress and strength changes; the stress changes which result from depletion, the stress-depletion response, are addressed in this paper. Stress-depletion responses from reservoirs in the Gulf Coast region and in the North Sea have been collated and show a range of stress reductions which fields undergo accompanying the field-wide pore pressure depletion. The stress-depletion response of a field only addresses the minimum stress changes, consequently, the maximum horizontal stress change accompanying depletion can only be estimated using models. The ability to predict the stress-depletion response of a field requires an understanding of what processes control the initial stress magnitudes, and the boundary conditions which the reservoir experiences during the production lifetime. The factors which define and influence the stress-depletion response of reservoirs are addressed, specifically the geological boundary conditions. The ability to model and predict the stress-depletion response of the reservoirs is then discussed, specifically focusing on the role and influence of the overburden surrounding the reservoir on the predicted response. Analytical and numerical models illustrate the influence of the material properties in the reservoir and overburden, and the reservoir size on the stressdepletion response. The ability to predict stress changes during depletion is erratic primarily due to insufficient data. Uncertainty in the pre-production estimation of the stress- depletion response of the reservoir has a considerable impact on the predicted stability of wells in the reservoir interval. The ability to determine an accurate stress-depletion response is a principal consideration for reliable stability predictions and design recommendations for horizontal and multilateral wells. P. 433
- North America > United States > Texas (0.94)
- Europe > United Kingdom (0.88)
- Europe > Norway > North Sea (0.67)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Fault > Dip-Slip Fault (0.46)
- North America > United States > Texas > Vicksburg Formation (0.99)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Alwyn Area > Blocks 3/8a > Greater Alwyn Fields (0.98)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Alwyn Area > Blocks 3/8a > Alwyn Area (0.98)
- (39 more...)
Abstract The rock mechanical behaviour of reservoir rocks is important in the design and implementation of drilling and production programmes. Traditionally rock mechanical properties are obtained from direct measurement on core samples or from mechanical calculations on acoustic wireline log measurements. This paper reports the rock mechanical properties of many different reservoir rocks of different porosities. This has led to the development of a new method of predicting rock mechanical properties directly from porosity. The paper discusses the measurement of experimentally derived porosity, elastic moduli and fracture strength parameters and the intetpretation of these mechanical properties results into direct correlations with porosity. The application of these results to obtain continuous rock mechanical property plots of the reservoir from wireline derived porosity is discussed. The practical use of these rock mechanical property profiles in drilling, production and enhanced reservoir simulation is also emphasised. Porosity (), modulus of elasticity (E), Poisson's Ratio (v), uniaxial compressive strength (UCS), cohesion (), angle of internal friction (), and triaxial stress factor (k), were measured on samples from a wide range of North Sea reservoirs using a conventional triaxial testing machine. This paper describes the procedure used and presents the correlations obtained from plotting each of the rock mechanical properties against porosity. The derivation of wireline porosities along with empirical corrections are presented and the results of applying the correlations to these wireline derived porosities to produce continuous rock mechanical property plots are discussed. Logs were calibrated to core-measured values to reveal realistic elastic and inelastic moduli profiles. The continuous property logs provide a reasonable estimate of the possible behaviour at discrete points throughout the reservoir interval, but they are limited in their description of the behaviour of individual beds as coherent bodies. A technique has been developed to pick out these individual beds and assess how they will perform as Rock Mechanical Coherent Units, i.e. sets of beds that perform in a similar or dissimilar manner to adjacent layers. Finally a discussion on how the results are used to aid production and generate enhanced reservoir simulation will be presented. P. 169
- Europe > United Kingdom > North Sea (0.26)
- Europe > Norway > North Sea (0.26)
- Europe > North Sea (0.26)
- (2 more...)
- Research Report (0.54)
- Overview (0.54)
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Well Drilling > Wellbore Design > Rock properties (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)