| Popis: |
The recent and dramatic increase in direct fracture mapping has profoundly altered our understanding of how fractures really do grow. New fracture-mapping technologies have allowed us to often directly measure what we could previously only model or assume. However, perhaps the greatest limitation of these new direct fracture-mapping technologies (tilt and microseismic) is the need for a nearby offset well in which to deploy instruments. In many environments, most notably offshore, there is often no feasible way to employ an offset observation well. Treatment well tilt mapping uses the fracture (injection) well itself as the "observation" well. The goal, quite simply, is to expand the range of environments where direct fracture mapping can be performed. The concept is simple: if fracture-induced deformation can be measured thousands of feet away at the surface or in offset wells, then it most certainly can be measured in the fracture well itself. The measurement of fracture-induced tilt versus time and depth (via an array of 4 to 20 tiltmeters) can allow robust real-time mapping of fracture height and width. Fracture length is then "modeled" based on observed height and width, and inferred fracture fluid efficiency. Treatment well tilt measurements can also provide direct measurement of mechanical fracture closure aiding, among other things, the estimation of formation closure stress. Mapping from the treatment well brings its own set of limitations and challenges. One is conducting minute wellbore movement measurements in the midst of a highvelocity flow stream. We have solved this challenge. Field data shows that the fracture-induced tilt signals in the treatment well are several orders of magnitude higher than those measured in offset wells, and they are much greater than the fluid-motion noise. The trickier challenge is deploying tools in a well during the pumping of proppant. So far we have performed real-time treatment well mapping only on fractures with clean fluid (i.e., no proppant), however, efforts are underway to overcome the difficulties with proppant. This paper provides an overview of the basic concepts, shows some real-data from treatment well applications, and presents one brief case study. |
