MAPPING FLUID FLOW IN A RESERVOIR USING TILTMETER BASED SURFACE DEFORMATION MEASUREMENTS

This paper documents the application of surface tilt monitoring to optimize reservoir management. Fluid injection into or withdrawal from a reservoir causes the earth to deform; tiltmeters are uniquely able to measure this deformation (tilt) with high spatial and temporal resolution. Surface tiltmeters, along with GPS information, are successfully being used primarily to monitor surface movement due to reservoir deformation, in real time, and the created subsidence data is correlated to individual reservoir events to provide advance warning before any damage occurs. This is the first documented application of surface deformation to map volumetric fluid movement within the reservoir.

This paper discusses the design and installation of tilt monitoring arrays and describes how surface deformation (displacement or tilt) data can be used to determine the volumetric deformation at the reservoir level. A poroelastic model is presented to calculate the reservoir deformation due to fluid migration along with a linear geophysical model to invert for the reservoir volumetric deformation from the measured surface deformation. Constraints are added into the procedure to better resolve the inversion problem as needed. After each inversion, the deformation at any location could be calculated from the inverted volumetric deformation distribution which best fits the measured deformation data on the surface.

The inversion technique was first validated using synthetic data and then applied to real data from cyclic steam injection into a pad of horizontal wells. The results indicate that continuous tilt based reservoir volumetric deformation monitoring is very useful in identifying areal fluid distribution during the injection cycle and preferential areal fluid withdrawal during the production cycle. This deformation information can also help in optimizing field development by providing a better understanding of the cyclic steam recovery process. Finally, the measured reservoir deformation can be directly used to calibrate a coupled geo mechanical reservoir simulation model to better predict the field behavior.