Weakly Cemented Sandstone Reservoir Sand Production Mechanism

This paper synthetically analyzed various data about weakly consolidated sand formation, and established theoretical models and methods studying on the sand production mechanism and analyzing the sand production trend for weakly consolidated sand formation qualitatively and quantitatively, which employ logging information as support, and are based on rock mechanics fundamental theories. In the qualitative area, the linear-elastic analytical model was established, which employed the logging data as the input one, and by which the sand production trend can be judged and analyzed. Compared with the current and comprehensively used "C" formula method , the results indicated that the "C" formula method is not suitable for the judgement of sand production of weakly consolidated sand formation. In the quantitative area, the 3-Dfinite element mechanical model analyzing the sand production trend for weakly consolidated sand formation was established quantitatively, which employed the logging data as the input one too. By using of the models and methods established in this paper, the sand production area surrounding borehole can be qualitatively and quantitatively calculated, which is the basis for the perforation completion, and delays the non-sand production period of oil wells, compared with the finite element method currently used, the 3-Dfinite element model also considered the effect of gravity and temperature.Through collection, analysis and comparing large amount data about weakly consolidated sand formation, we get that most weakly consolidated reservoirs are delta facies, fluvial facies and alluvial fan, and the separating and collection of particles are not good enough, and the consolidating manners of weakly consolidated sand reservoirs mainly are contacting and pore consolidating methods, and the cement is clay mainly, so it is sensitive to the fluid entering into formation .as for weakly consolidated formation, it is usually buried relatively shallow, and has high porosity and permeability.By using of the theoretical models established in this paper, the effects of in-situ stresses, reservoir pressure, well trajectory and perforation orientation on sand production of weakly consolidated sand formation were studied qualitatively and quantitatively. The results indicated that weakly consolidated sand formation, compared with well consolidated one, is sensitive to the change of stress in formation, owing to its weakly consolidated and low intensity formation, whether vertical well or deviated well, whether open hole or perforated hole, the in-situ stresses will directly influence the sand production of loose sand formation. Because of theAbstractheterogeneous of in-situ stress, some area around borehole will suffer much higher stress than other area, which even leads to shear yield and sand production in the area prior to other area , and the more heterogeneous of in-situ stress, the more sand production. So, in order to prevent from sand production and delay the span of production for oil wells, the well trajectory and perforation completion should be optimized, considering the requirement of production capacity and sand prevention. -Reservoir pressure also affects sand production, when reservoir pressure keep constant, increasing production pressure difference, the trend of shear yield and sand production of perforation hole will increase. With the depletion of reservoir pressure, the formation that does not produce sand originally may produce sand. So for the formation which may possibly produce sand , scientific and reasonable production method ought to be applied, and the production method also should be adjusted appropriately, so as to decrease the possibility of sand production.Up to now, there is little report on the effect of gravity on sand production, some research suggested that the effect of gravity on sand production can be ignored. The results in this paper indicated that gravity should be considered while studying on sand production of weakly consolidated sand formation. As for...