Systematic Use of Tidal Effects for Reservoir Appraisal and Well IntegrityMonitoring in a Near-Coast Onshore Environment

摘要

Tidal effects in wells have been observed for millennia and have been analysed since the 1970s,followingthe introduction of high-resolution pressure gauges.Tidal effects are usually more obvious offshore andmany papers focus on offshore wells with large tidal signals.This paper demonstrates that pressure changescaused by ocean tides are detectable in near-coast land wells and that,with careful analysis and processing,provide valuable additional information for reservoir characterisation.This paper uses a set of observations from multiple near-coast land wells with extended pressure historiesacquired as part of campaign of production and interference testing for reservoir characterisation purposes.These pressure records have variable tidal signal and data quality.A variety of methods have been publishedto smooth tidally influenced pressure data and extract or remove the tidal component.These different tidalfiltering techniques are tested on real data,and a preferred data processing procedure is selected appropriatefor the large quantity and variable quality of data in the study area.The methodology allows data frommultiple wells to be quickly processed and consistently screened.This paper gives examples of tidal behaviour in selected wells and compares the results across multiplewells in the study area to show how identification of subtle tidal effects is useful for:1.Field appraisal of a saturated oil-rim with gas cap by examining differences in tidal amplitude inwells in different parts of the field.2.Estimation of critical gas saturation by comparing tidal amplitudes before and after an extendedwell test.3.Monitoring well integrity in a producing field by tidal analysis of annular pressures.The paper also recommends a reservoir surveillance programme to obtain useful tidal data in onshorewells.This paper will be useful to engineers attempting to find and interpret subtle tidal data,instead of simplyremoving it.It recommends a systematic approach for using tidal data in wells where tidal signals are smalland/or gauge resolution is poor,based on experience with real data with variable data quality.It also providesa case study to show the value and practical application of a surveillance programme to identify tidal datain near-coast land wells.