Introduction Summary For the past several years, Total has been developing different applications of microseismic monitoring in the E&P domain, such as structural definition for exploration, reservoir fracturation (frac) monitoring, gas or steam injection monitoring and field production monitoring. This procedure is mainly based on feasibility studies that allow the optimization of both acquisition layout/parameters and estimated accuracy of the results. A structurally-focused acquisition is planned on the Tempa Rossa field (Italy) for Q2 2007 and gas injection tests in the Middle East and South America are also planned for 2007.
The application of microseismic analysis is presently concentrated in the domain of frac monitoring, but it can also be useful for field development. This paper describes different approaches that Total is testing in order to appreciate how the analysis of microseismic events can benefit an E&P petroleum company.
Field monitoring case 1 : gas injection monitoring Exploration purposes It can be difficult to imagine what the analysis of microseismic events can offer for exploration purposes, whereas 2D or 3D reflection seismic is supposed to give a precise and reliable image of the subsurface. However, while in complex areas as thrustbelts the acquisition of conventional 3D seismic can be prohibitively difficult and expensive, the abundance of natural seismic events makes microseismic studies an attractive alternative. For the past 3 years, Total has been investigating the possibility of performing a passive seismic acquisition on the Tempa Rossa field (Figure 1) in southern Italy (Apennines) in order to refine the structural definition of the heavy oil field and knowledge of its oil content. The overall objective of the study is a better definition of the structural scheme and eventual delineation of different compartments by means of seismic event locations to be indicators of main faults expression in this tectonic complex area. Local seismicity up to magnitude -1 can be used for passive tomographic studies using P- and S-wave travel time phases. These natural microearthquakes recorded over several months by a mobile network of surface seismometers are used to provide a detailed 3D velocity and Vp/Vs image of the upper few km of the crust. This technique involves simultaneously inverting for microearthquake locations and making adjustments to the initial velocity model. Various feasibility studies were carried out in order to optimize the acquisition geometry and parameters. Acquisition is planned to start Q2 2007 with a duration of about 10 months if the pilot phase is successful. Results are expected mid-2008.
Different field monitoring approaches were tested specifically for injection purposes (steam, gas or water). The first step is to perform a microseismic feasibility study in order to define optimized layout and expected results. In the case of a producing carbonate reservoir (Arab-D) in offshore Middle East (Figure 2) the microseismic monitoring objectives are to better control the injection of gas and to evaluate the role of the faults and other reservoir heterogeneities during stimulation. As gas injection creates perturbations in pore pressure as aresult of shear stress failure along zones of weakness.