A New Approach to Subsurface Gravity

Summary The borehole gravity method can be applied to making Gravity Measurements While Drilling (GMWD) if an appropriate gravity sensor can be developed for use in a drilling environment. We performed a study to determine at a high level the potential value of developing GMWD for solving a wide range of important petroleum exploration and production (E&P) problems. The study investigated the potential applications of using GMWD to steer a drill bit. Although gravity measurements in mines have been performed since the early 1800s and the Borehole Gravity Meter (BHGM) has been in use since the early 1970s, prior to this study nobody had ever extensively looked at the subsurface gravity signatures of geologic structures before. What we discovered was quite surprising and has led us to believe that we may be at the beginning of a whole new geophysical method of subsurface gravity, comprising borehole gravity, GMWD, and embedded gravity sensors applied to smart field technology. We discovered that the subsurface gravity field associated with geologic structures is quite detailed and diagnostic. In fact, of the 20 E&P scenarios we investigated, we discovered that subsurface gravity could make a significant impact in 60% of them and some impact in an additional 25% of them. If a new gravity sensor is built that will have an order of magnitude more sensitivity over present technology, then subsurface gravity could have a significant impact on another 10% of the scenarios. Furthermore, we were surprised by the fact that our intuition did not serve us well. In several instances we thought that gravity would not be able to impact the objective of the scenario only to find out not only could it make a difference but also it could lead to an actual analytic solution to the problem. In a couple of instances we were sure subsurface gravity would work only to find out that it would fail completely.