Monitoring In Situ Processes

Introduction The theme of the 1986 CIM Petroleum Society Technical Meeting is Technology and Investment. This paper is an argument to invest in technology: the technology for monitoring in situ processes. Integrated project monitoring brings benefit in three ways; first, good monitoring information identifies critical in situ processes; second, such data validates assumptions made under conditions of extreme uncertainty; third, monitoring data can be used to control in situ processes. This paper reviews available methods, implementation, nature and precision of the data expected from each method, and interaction of the various methods. Some approaches to data acquisition and interpretation are discussed. The conclusion to the paper can be stated beforehand: a commitment to current technology is necessary; the potential benefits are large. Monitoring Strategies Fundamental to design and process implementation in earth materials is uncertainty. It cannot be eliminated; it can only be minimized to the limit of economy. There is uncertainty as to reservoir geometry, parameter value and functional relationships. There is also uncertainty as to process; all critical processes occurring in situ have not yet been identified, as suggested by recent literature (Dusseault and Simmons, 1982). There is even uncertainty of a random nature such as that associated with microscopic dispersion or Markovian processes. Uncertainty means that any deterministic modelling effort will yield one answer among a large number of possible answer, each with a different probability of occurrence. Often, only expensive post process methods are used (Joseph et al., 1983, Buxton, 1974), leaving great uncertainty as to the process sequence in the field. However, any stochastic (probablistic or statistical) modelling approach is also affected by the same uncertainty. The goals of monitoring are: to minimize uncertainty, to provide useful data to the design engineer and modeller; and to increase understanding of processes. For an individual project, monitoring from beginning to end may yield more oil, and will certainly yield more understanding which will generate economies in future projects. Monitoring and data interpretation cannot be performed in isolation; these tasks must be integrated with other project activities such as modelling, new well drilling, geophysical logging programs, and laboratory programs. Personnel associated with the project must be aware of the monitoring goals and be willing to cooperate in data management. Monitoring data are critically important; reliance on field data takes precedence over consideration of mechanisms based on experience, and over results of numerical simulation. It is the responsibility of odellers and conceptualists to postulate reasonable explanations for the data, not to deny it. Classification Of Monitoring Methods Monitoring may be active or passive. Active methods generate specific fields and evaluate them over space or time, or emit signals and measure changes in them. Passive methods measure fields generated by the process itself. Examples of the former are active seismic or CSAMT methods; of the latter, passive seismic or temperature monitoring. Monitoring efforts can be remote or proximal. Remote methods can be applied distant from the process; examples are surface deformation monitoring, tilt, and micro-seismic monitoring.