Job Description:

The analysis of drilling events - complicated walking of the BHA (overpulls, landing), pressure and torque surges in the intervals of borehole reaming, as well as the presence of collapse sludge, showed that the cause of complications is the collapse of the trunk in the area of articulation of the parent and lateral boreholes.

To solve the problem, three-dimensional geomechanical modeling of the near-well space near the articulation zone was carried out. The stability of the borehole was calculated for various cutting parameters (Fig. 1):

Fig. 1. The interval of the articulation zone of the main and lateral borehole for the planned trajectory with the display of the calculated grid of variable pitch

• orientation of the mother borehole relative to horizontal stresses;
• the location of the lateral borehole relative to the mother borehole (direction and intensity of cutting);
• different borehole diameters;
• different values of the specific mud weight and, accordingly, the pressure in the well above and below the reservoir pressure.

During the study, the elastic ideally plastic Mohr-Coulomb model was chosen as the main model of rock behavior. The coefficient of stability margin at each point of the array (including on the wall of the articulation and the well) was obtained from the fracture criterion:

where the cohesion is C, UCS is the uniaxial compressive strength, TSTR is the tensile strength. Thus, Kstab ≤ 1 characterizes the areas of extreme deformation of rocks, i.e. the zones where the destruction of the rock will occur.

To evaluate and visualize the results of the analysis in the form of sensitivity, the parameter ∆ was developed, defined as the ratio of the current diameter of the well to the length of the fracture interval of the bridge (Fig. 2). The combination of the largest possible angle between the trunks (taking into account technological limitations) and the direction of cutting down or close to it gives minimal destruction between the boreholes.

Fig. 2. Stereonet sensitivity ∆ to the angle between the boreholes and the direction of cutting from the mother boreholes.

Result:

During the construction of multi-lateral wells, complex three-dimensional modeling of the articulation zone, taking into account the results of one-dimensional modeling of mechanical properties, pressures and stresses, allows you to determine the optimal azimuths of horizontal sections, intervals, intensity and cutting directions, and avoid complications during well construction.