Borehole pressure, maximum

Surface Equipment 1101. When and How to Close the Well 1101. Gas-Cut Mud 1103. The Closed Well 1105. Kick Control Procedures 1106. Maximum Casing/Borehole Pressure 1111. 

The guiding principle of all these techniques is that bottomhole pressure is held constant and slightly above the formation pressure at any stage of the process. To choose the most suitable technique one ought to consider (a) complexity of the method, (b) drilling crew experience and training, (c) maximum expected surface and borehole pressures and (d) time needed to reestablish pressure overbalance and resume normal drilling operations. 

The water injection pressure, seepage velocity and wetting effect distribute intensively in the borehole under the water injection arrangement of 80 m length hole under the condition of 20 MPa pressure have the same variation characteristics with 50 m length hole. Pressure decay by 76.97% in the scope of the drill hole radial 7.5 m under 20 MPa pressure, maximum seepage speed reach more than 14.52 m/s, and the minimum velocity is 2.9 m/s, the water addition distribute between 13% - 1%, and its minimum addition is 1.2%. 

Dissolved Gas. Gas which enters the borehole when penetrating a high pressure zone may not dissolve immediately in the mud. The free gas considered here is the gas entering the borehole minus the dissolved gas. Table 4-128 indicates the maximum volume of dissolved gas at bottomhole conditions expressed in percent of annulus mud volume. Thus, when entering a high pressure permeable formation this much gas will dissolve first before free gas appears in the mud. 

Confining pressure of 1.0 MPa at the right borehole slightly decreases the maximum stresses of the confined borehole wall, but the effect seems to be limited. 

Monitor borehole flow and pressure first if possible (it may not be possible with some flow meters). Attach monitor to gas tap and then open gas tap and record maximum flow and pressure and then any reduction that occurs and over what time. Record flow rafe and pressure for a minimum of one minute and record maximum, minimum and average readings. 

---