Estimating Geo-Mechanical Strength of Reservoir Rocks from Well Logs for Safety Limits in Sand-Free Production (original) (raw)
Related papers
International Journal of Innovative Science and Research Technology, 2024
Sand production in the Niger Delta oil region is one of the most difficult challenges encountered during the many stages of field development planning, resulting in expensive drilling, production costs, and damage to oil installations. This geomechanical problem is expected because the Niger Delta Province is dominantly a loosed sandstone terrain, and the sand grains are highly friable. The study centres on employing empirical relationships of rock mechanical parameters from wireline logs to predict the vulnerability of lithologic formations to sand production in a reservoir in the Niger Delta. The reservoir five sandstone units were first recognized by using wireline logs (Gamma ray and self-potential logs), and the fluids were differentiated using resistivity, porosity, and density logs. The identified hydrocarbon prospecting sands were correlated throughout the five (5) wells. Gamma ray, resistivity and porosity logs were used for the correlation. Shear and compressive wave from the sonic log were then used to derive the rock mechanical parameters (Poisson ratio (ν), Young modulus (E), shear/rigidity modulus (G), bulk and matrix/grain moduli (Kb and Km), bulk and grain compressibility (Cb and Cr), Unconfined compression strength (UCS) and Critical flow rate pressure (CFRP). Four Prediction of Sand Production indicators (Formation sanding indicator method, Schlumberger formation sanding indicator, Bulk Elastic Modulus Ratio and Composite Modulus Estimation) derived from the rock mechanical parameters were used to adequately analyse sanding. The analysed reservoir exhibits sandstone units with lower value of Poisson ratio, Bulk modulus, Young’s modulus, Shear modulus and Unconfined compression strength of 2.3GPa, 0.26, 11.2GPa, 7.93GPa, and 16.73MPa, respectively. The formation shale exhibited higher values of Poisson ratio, indicative of its ductile nature that is resulting mostly from its clay content; the Bulk modulus, Young’s modulus, Shear modulus, and Unconfined compression strength exhibited high values (8.23 MPa,0.37,17.08 MPa, 25.02 MPa, 66.22 MPa respectively) while porosity and compressibility showed decreased values (0.07, 0.08 Mpa-1 respectively), leading to enhanced stiffness due to elevated moduli, hence less prone to deformation than the loosed sandstone units. The results of the four (4) Prediction of Sand Production models indicate a high risk of sanding during production of the investigated reservoir. A Critical flow rate pressure (CFRP) of 18.30 MPa is predicted to mitigate against sanding in the wells if the critical flow rate during production stays below 18.30 MPa. Thus, this research application of empirical relationships derived from rock mechanical parameters and wireline logs in predicting sand production can effectively aid informed investment decisions, risk assessment and performance optimization in Niger Delta reservoirs.
A New Mechanical-Hydrodynamic Safety Factor Index for Sand Production Prediction
Energies, 2021
A new applicable safety factor index (SFI) was developed to identify the impact of mechanical stresses and hydrodynamic forces on the potential sanding of a sandstone reservoir. The SFI is calculated by a fully numerically coupled analysis of the mechanical deformation and hydrocarbon fluid flow in the sandstone formation via FLAC3D software, Itasca Consulting Group, Minneapolis, USA. Sand production is commonly ascribed to mechanical failure while the influence of hydrodynamic forces on sandstone erosion is neglected or underestimated. However, the new SFI enables the designer to quantify the impact of mechanical and hydrodynamic forces separately on the future occurrence of sanding. Quantitative comparison is a beneficial tool to choose the most appropriate layout of the wellbore and perforations. The results demonstrated that hydrodynamic forces may have a more significant effect on sand production than mechanical stresses. Furthermore, the sanding process does not necessarily co...
An Empirical Correlations to Predict Shear Wave Velocity at Southern Iraq Oilfield
Journal of Petroleum Research and Studies, 2022
Geomechanical studies are very important in the development stages of oil fields to solve many problems such as wellbore instability and sand production. However, this study is not complete without the availability of mechanical properties of rocks. These properties estimate from petrophysical logs based on the compressional and shear wave velocities. But the shear wave is often missing from most wells, and the reason might be cost-saving. Therefore, this study aims to find correlations to predict the shear wave velocity of the Mishrif reservoir. The empirical equations are formed using log data of six wells drilled in the southern Iraq oilfield. The Statistical Package for the Social Sciences (SPSS) software was relied on to find the empirical correlations. Eleven empirical equations have been obtained, but the best are three equations: linear, quadratic, and cubic because they give the highest value of R2 = 0.924. Also, these three equations (linear, quadratic, and cubic) have bee...
An analytical model to predict the volume of sand during drilling and production
Journal of Rock Mechanics and Geotechnical Engineering, 2016
Sand production is an undesired phenomenon occurring in unconsolidated formations due to shear failure and hydrodynamic forces. There have been many approaches developed to predict sand production and prevent it by changing drilling or production strategies. However, assumptions involved in these approaches have limited their applications to very specific scenarios. In this paper, an elliptical model based on the borehole shape is presented to predict the volume of sand produced during the drilling and depletion stages of oil and gas reservoirs. A shape factor parameter is introduced to estimate the changes in the geometry of the borehole as a result of shear failure. A carbonate reservoir from the south of Iran with a solid production history is used to show the application of the developed methodology. Deriving mathematical equations for determination of the shape factor based on different failure criteria indicate that the effect of the intermediate principal stress should be taken into account to achieve an accurate result. However, it should be noticed that the methodology presented can only be used when geomechanical parameters are accurately estimated prior to the production stage when using wells and field data.
Evaluation of Geomechanical Parameters for Sand Prediction in Apogee Field Offshore, Niger Delta.
Volume 3 of 1, January , 2022
The research focuses on the evaluation of geomechanical parameters for sand prediction in APOGEE, offshore Nigeria. Depletion of reservoir, increased water- cut, reservoir ageing, poor completion and poor reservoir management all causes sand production. Sand production increases the cost of maintenance of a well, leads to well shut in and jeopardizes the safety of worker. Four wells were evaluated using geomechanical parameters and well logs data (sonic log, Gamma ray, density, resistivity, and neutron log). Furthermore, six reservoirs were identified (reservoir 1- 6) and correlated across the five wells. Shear and compressive wave travel time from the sonic log were obtained and were used to estimate geomechanical parameters (both elastic and inelastic). The estimated geomehcanical parameters includes Poison ratio, Young modulus, Bulk modulus, UCS and pore pressure. Four methods were used to evaluate the sand potential and they include: B-index, Schlumberger index, Bulk modulus, Compression ratio and combined ratio. The analysis revealed a strong linear relationship between UCS and porosity with a regression coefficient correlation between 1 and 0. 98. This research shows the studied reservoirs falls below the threshold pressure for sand production. Comparing the four methods, the ratio of Shear modulus to the bulk compressibility ratio (G/Cb) method predicted the highest potential for sand production. This research therefore validates that reservoirs in APOGEE field is highly unconsolidated. Keywords: Poison ratio, Young modulus, Bulk modulus, UCS and Pore pressure and Sand control.
Journal of Engineering
Shear and compressional wave velocities, coupled with other petrophysical data, are vital in determining the dynamic modules magnitude in geomechanical studies and hydrocarbon reservoir characterization. But, due to field practices and high running cost, shear wave velocity may not available in all wells. In this paper, a statistical multivariate regression method is presented to predict the shear wave velocity for Khasib formation - Amara oil fields located in South- East of Iraq using well log compressional wave velocity, neutron porosity and density. The accuracy of the proposed correlation have been compared to other correlations. The results show that, the presented model provides accurate estimates of shear wave velocity with correlation coefficient of about unity than other currently available methods.
Sand Prediction by Different Criteria and a Validation by a Perforated Test in a Sandstone
SPE Heavy Oil Conference Canada, 2012
The onset of sand production in a hollow cylinder test is evaluated by three different sanding models, i.e. shear failure, cohesive tensile failure, and EPS (Equivalent Plastic Strain) failure. The comparison of the results with experimental results from a hollow cylinder test shows that the shear failure model provides the most conservative prediction, while the EPS can provide the closest results to those from the test.
A New Concept of Sand Production Prediction: Theory and Laboratory Experiments
SPE Drilling & Completion, 2000
Summary Conventional theories of sand production prediction distinguish between compressive (shear) cavity (perforation, borehole) failure, induced by a combination of in-situ stress and drawdown, and tensile cavity failure, induced by the near-cavity pore pressure gradient. In this paper we show, using a global criterion for strain localization around the cavity (i.e., cavity failure), that in most cases the preference for either compressive or tensile cavity failure only depends on the cavity size and on the constitutive properties of the rock, and not on effective near-cavity stress or the pore pressure gradient. It is shown that "large" cavities (e.g., boreholes) always fail in compression rather than in tension failure. Only for sufficiently small cavities (e.g., perforations) in weak, moist sandstones, is compressive failure supressed and tensile failure possible. The above results deviate significantly from previous sand production prediction concepts. They are furt...
Steady-State Strength, Relative Density, and Fines Content Relationship for Sands
Transportation Research Record, 1996
The appropriate choice of shear strength of liquefied sands is an important component in seismic slope stability evaluation. Several factors affect the undrained steady-state strength (S us) of sands. The steady-state strengths of 24 sandy soils were analyzed. It is shown that fines content, relative density, and friction angle play important roles affecting S us. Fines content was found to be the major factor affecting S us. This was verified experimentally for one sand. When the S us data for sands were grouped into (a) relatively clean sands (Ͻ12 percent fines), (b) silty sands (12 to 50 percent fines), and (c) silts or sandy silts (Ͼ50 percent fines), at the same relative density, relatively clean sands showed the highest S us. Silts showed the lowest S us. Silty sands showed intermediate strengths. Lower-bound S us-relative density relationships were established for relatively clean sands and silty sands. The appropriate choice of shear strength of liquefied sands is an important component in seismic slope stability evaluation. It is well recognized that several factors may significantly affect the in situ postliquefaction shear strength of sands. At present, it is mostly determined by three methods: (a) steady-state strength (S us) testing in the laboratory, followed by making appropriate corrections to the field void ratio condition taking relevant factors into account (1), (b) back-calculated residual strength (S r) correlation with equivalent clean sand standard penetration test blow count [(N 1) 60-CS ] on the basis of past case studies (2,3), and (c) the normalized strength ratio approach (4-6). The S us approach for seismic stability analysis is based on the assumption that seismic flow deformation is affected primarily by one mechanism, based on the concept of steady-state deformation (1), except for possible differences due to the shearing mode. If the back-calculated S r data are also affected only by the latter mechanism, then practically, S r and S us should be the same, except for possible differences due to stress path effects. In a real field problem several mechanisms (2,7-9) may influence the operative strength. The back-calculated S r (2) may collectively reflect the effects of different mechanisms, if present, in each case history. At present the relationship between S r and S us or their relationship with postliquefaction strength is not clear. In general, past studies (2) indicate that the back-calculated residual strengths are smaller than typical laboratory S us values obtained for different sands at comparable relative densities. It is suspected that different mechanisms that might have been operative under given site conditions could have affected the residual strength, accordingly resulting in a different S r compared with the S us (2). There is concern among practitioners that the use of S us determined from laboratory tests may be unsafe (10). Having observed such differences, in general, there is consensus among researchers that within the limitations of current understanding of the factors affecting the postliquefaction strengths of sands,