Field Application of a Novel Core-based In-Situ Stress Estimation Technique

摘要

In this paper, we present the first field application of a novelrnmethod to estimate in-situ rock stress. This technique, whichrnwe have baptized "PKM (Pestman-Kenter-vanMunster)rnmethod", uses Acoustic Emission-controlled polyaxialrnreloading of core in the laboratory. The method worksrnanalogous to the Kaiser effect that is observed when reloadingrnalong a single stress axis. Contrary to other Acoustic Emissionrnmethods, our novel approach is likely to measure present-dayrnstresses, even if the core has been subjected to paleo-stressesrnthat are higher than the present day stresses . Proof of conceptrnof the method has been provided using extensive experimentalrnwork on outcrop sandstone (which was subjected to a stressrnpath simulating burial, coring and core retrieval to surface), arnsimple analytic model and numerical simulations using a 3Drndiscrete particle method.rnRecently, the method was applied for the first time on realrncore material, a preserved sandstone core from thernMunnekezijl field (onshore gas) of NAM (NederlandschernAardolie Maatschappij) in The Netherlands. An advantage ofrnfirst application of the technique to this field was that therernwas availability of good quality stress estimates (for the samernlayer as where our core was taken) obtained from otherrnmethods. A study including hydraulic frac data and boreholernbreakout shape had been performed in the past to estimate thernmagnitudes of the major and minor horizontal effective stress.rnHence, the results of our method could be compared to otherrngood quality data.rnThree samples have been cut from core taken at a depth ofrnsome 4000 m [13000 ft] in the Munnekezijl field, forrnapplication of our PKM method. Only the weakest samplernshowed a clear stress memory effect, and was used for stressrnestimation using our method. The results compared veryrnsatisfactorily with the estimates from the hydraulic frac datarnand borehole breakout analysis. Although this is only the firstrnapplication, and further validation is needed, these resultsrnshow a clear promise of the PKM method.