CNOOC is operating in YingGehai Basin and QiongSouthEast Basin of South China Sea. Formation testing has been routinely used by this operator in field exploration to confirm hydrocarbon presence, define the hydrocarbon type as well as getting PVT samples. Due to the high cost of DST operation in the offshore environment, formation testing is considered as the main testing method to test the small to medium size sand bodies. And the result is accepted to claim reserve of hydrocarbon. As the recent offshore exploration has focused more on deeper formation where the sand permeability is between low to ultra-low, the pressure pretest mobility is easily lower than 1md/cp. In some particular formation, the formation mobility is even lower than 0.1md/cp. For this type of permeability of sand, testing becomes very difficult and getting fluid sample to claim reserve becomes a huge challenge. If the formation tester fails to obtain the samples, very often the later DST operation would not achieve a success. A new probe module of formation tester has been introduced to the industry early 2013 and it has been designed to perform formation testing in low permeability environment. Especially it could apply a much higher drawdown than previous technology to move the tight hydrocarbon. In this paper, a few cases will be presented to demonstrate how this new probe work in Yinggehai and QiongSouthEast basins fluid sampling operation where we sampled successfully at formation with the mobility is less than 0.1md/cp. With this result, great amount of reserve can be claimed and this new probe has been considered as the unique solution of testing these formation as well as predicting the possible production capability..

Cavernous carbonate formations are characterized by strong heterogeneity, which results in the complex electric logging responses and the difficulty in the logging identification and evaluation. Numerical simulation of electric logging tools is helpful to figure out the logging response characteristics in these formations and could provide theoretical support for cave recognition and evaluation. In this paper, based on three dimensional finite element methods, a local refinement technique is adopted for the accurate discretization and simulation of complex sphere caves. Then, the response characteristics and sensitivity of dual laterolog to caves around and penetrated by wellbore are analyzed, finally the differences of sensitive scope between deep and shallow laterolog are studied. The results show that the dual laterolog response decreases significantly when cave exists. Affected by cave boundary and the investigation depth of dual laterolog tool, the logging response for caves penetrated by wellbore is very complicated, however it exhibits parabolic‐like characteristic for caves around wellbore. Compared with caves around wellbore, the dual laterolog is much more sensitive to caves penetrated by wellbore. For caves around wellbore, the maximum sensitive distance for deep and shallow laterolog between the cave boundary and well wall is 0.5 m and 0.3 m, respectively.

No abstract