FLOW UNIT DETERMINATION THROUGH LITHOFACIES IDENTIFICATION AND ITS RELATIONSHIP WITH PETROPHYSICAL AND DIAGENETIC PROPERTIES IN EARLY EOCENE RESERVOIRS, CHICONTEPEC BASIN, MEXICO

摘要

The use of high technology well logs with the enough resolution to obtain in-situ information of the Upper Paleocene - Lower Eocene clastic hydrocarbon reservoirs at the Chicontepec Basin, in addition to the laboratory core analysis of conventional core samples, has been of crucial importance in the identification, classification and discrimination of the different flow units at well scale and in a specific field. The greater understanding of the dynamic and rheological processes that take place in the gravitational flows of underwater sediments (classical and hyperpycnal turbidites), gained due to the direct observation of the outcrops as well as the experience carried out in the laboratory flume tank with sedimentladen stream flows (experimental short-lived and quasisteady turbidity currents), has enabled us to determine the specific occurrence of the different types of expected lithofacies in basin ward direction: from the more channelized zones to the most splayed zones (lobes). In this way, we can understand the facies tract to be expected for each event at field scale and for a particular reservoir. Thus the facies analysis bears a highly predictive character which was previously underestimated in the classical sedimentology studies. We show that there is a specific relationship between the type of sedimentary lithofacies and its primary petrophysical property. Obviously the diagenetic processes and the degree of compaction can act against or on in favor of this initial relationship. Thus, any study of primary lithofacies should necessarily involve its subsequent diagenetic history, since the final petrophysics quality of the determined lithofacies will depend among other variables on: the type and mineralogy of the source, the confining stress, the packing degree as a function of the sedimentary structure as well as on the primary sediments; including the sediment sorting as a direct consequence of the flow efficiency and segregation. We present a study case in Agua Fria field from Chicontepec Basin in which we analyzed the relationships among lithofacies, subsequent diagenesis and final petrophysical results, that can be used as an example of flow unit determination with a great detail at both well and field scales, and which is recommended to be applied also in other analogous areas of the same basin.