Production history, fluid pressure and uniaxial compressive strength are basic data to evaluate the risk of sand production. Evaluations of the compressive strength based on logs are illustrated for the example of a well on the Germigny-sousCoulombs structure. Then relationships between compressive strength and porosity are developed using a theoretical approach of grain contacts, the analysis of published rock mechanics data and mechanical measurements on plugs taken from well cores. It is shown that compaction factor can complement porosity in the analysis. A field example illustrates the relationship between a critical differential pressure and compaction factor or porosity.
Production history, fluid pressure and uniaxial compressive strength are basic data to evaluate the risk of sand production. Evaluations of the compressive strength based on logs are illustrated for the example of a well on the Germigny-sous-Coulombs structure. Then relationships between compressive strength and porosity are developed using a theoretical approach of grain contacts, the analysis of published rock mechanics data and mechanical measurements on plugs taken from well cores. It is shown that compaction factor can complement porosity in the analysis. A field example illustrates the relationship between a critical differential pressure and compaction factor or porosity. Introduction The general frame of this study is the production of oil and gas from poorly consolidated formations. It is well known that such a production can be hindered by the phenomenon of sand production. Various gravel-pack equipment can be used to prevent sand production but they are costly and generally harmful to well productivity. Therefore the decision to use such equipment has considerable economic impact and requires a clear-sighted evaluation of the risk of sand production. Tensile rupture and compressive rupture are proposed as possible mechanisms of sand failure. Tensile rupture is possible under two conditions:the fluid pressure gradient at the production face is larger than the gradient of the radial stress,the tangential effective stress does not exceed the level of compressive failure (less than ucs). As fluid pressure and tangential effective stress are linked through the equilibrium equation of the sand, conditions (a) and (b) impose an upper limitp max to the pressure difference Pd - Pw through the zone drained by a perforation. p max is proportional toucs and various values of the ratio p max/ ucs can be found depending on the drainage geometry (radial, spherical) and on the production history (influence of shut-in periods). Compressive rupture is also possible if, under symmetrical conditions: the pressure gradient remains smaller than the gradient of the radial stress, the effective tangential stress reaches theucs critical level. To these conditions corresponds a maximum of the total depletion ptd which depends linearly on ucs. The field observations apparently confirm the general trends of these theoretical analyses. For example satisfactory production conditions are obtained if the drawdown pressure Pdd is maintained under 0.5 ucs. Therefore using theoretical modelling and field observations two categories of data appear to be very important: pressure data characterizing the production history and the fluid flow as well as data characterizing the uniaxial compressive strength of the rock. P. 381^
It is useful to map hydraulic fractures in order to improve the rate of success of such operations and to optimize the pattern of stimulated wells. The proposed method can be used during a minifracturing or prefracturing operation and necessitates a downhole 3D acoustic detector clamped in the well. A few to a few dozen cubic meters of gel are injected during fracturing phases, and the acoustic activity is recorded after every injection. Then signals containing apparent P and S waves are analyzed to determine the directions and distances of the emitting sources. A number of arrivals cannot be interpreted easily, in particular those corresponding to refractions along the casing.Three field examples corresponding to a vertical, a deviated and a slant well are given. Knowing the P and S wave velocities in the different layers and a careful choice of the tool position are essential to the success of the method.
International audienceA short term performance assessment methodology under development and validation at the In Salah CO2 storage site is presented. The progressive approach first concludes of the necessity to consider a dual media reservoir system at Krechba to fit with gas reservoir production, CO2 injection and CO2 breakthrough at an old appraisal well (Kb-5). To improve gas migration prediction while also considering the geomechanical behavior of the site, an extended geomodel has been developed. Fluid pressure simulation results representative of the dual media reservoir model and of the simple medium upper layer ones (up to the water table) are used to initiate the geomechanical modeling. Comparison of the preliminary geomechanical simulation results assuming a poro-elastic behavior and InSAR satellite surface displacement data are coherent and in the same order of magnitude (∼20 millimeters at maximum displacement)
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