Once drilling commences, data of many types are recorded which can be monitored to help re-calibrate the pre-drill well plan. These data include mud-weight, D-exponent (a calculated relationship based on data such as weight on bit, rate of penetration etc.), connection gas, cuttings, torque, mud temperature in and out, bit size, and caliper. In addition Logging-While-Drilling (“LWD”) velocity and resistivity data could be part of a Bottom-Hole Assembly (BHA) which, in conjunction with a normal compaction trend defined by analysis of previously drilled wells, can be used to monitor the pressures encountered whilst drilling ahead. Read more.