The author justifies the need to take into account the simultaneous operation of several oil-gas-water saturated reservoirs opened by the borehole when calculating surface casing setting depth in order to eliminate the possibility of fracturing under the surface casing shoe in the case of gas, oil and water showings after the complete replacement of drilling mud in the wellbore with a reservoir fluid or a mixture of fluids of different horizons and well capping. A method is given for calculating the average specific weight of formation fluids in a well in the case of open blowing. It is shown that if a well breaks down several reservoirs, then in case of open blowing, all reservoirs, including aquifers, will be consistently connected. In this case, the well will be filled with a mixture of reservoir fluids from different horizons. The fluid share of each horizon in the mixture will be determined by the coefficients of reservoir productivity and the depression of each reservoir. The initial data for the calculation are the reservoir pressure, the depth of the reservoir, the coefficient of productivity, the specific gravity of the fluid for each horizon opened by the well. To calculate the average specific weight of a mixture of formation fluids in a well, it is necessary to solve a system of equations using numerical methods. It is shown that in calculating the surface casing setting depth in case of opening several oil and gas-saturated reservoirs, it is necessary to take into account the average specific gravity of reservoir fluids in the well over all the reservoirs, the depth and the reservoir pressure of the reservoir with maximum value of differential pressure (and not the maximum gradient of the reservoir pressure), the specific gravity of the gas and the saturation pressure of oil with gas are taken through the reservoir with the maximum pressure of saturation of oil with gas. It is shown that when taking into account the work of several reservoirs, the calculated surface casing setting depth can be both smaller and larger than when calculated per individual reservoir.
1. Federal norms and rules in the field of industrial safety “Pravila bezopasnosti v neftyanoy i gazovoy promyshlennosti” (Safety rules in the oil and gas industry), URL: http://docs.cntd.ru/document/4990110042. Kayugin A.A., On a calculation of surface casing pipe rih depth and the presence of several oiland water-saturated layers in the cross-section (In Russ.), Neft'. Gaz. Novatsii, 2018, no. 11, pp. 48–51.