Analogous Reservoirs to Chicontepec, Alternatives of Exploitation for this Mexican Oil Field

Abstract

Abstract The giant Chicontepec field contains oil from 18 to 45 oAPI in laminated sandstones of 0.1 to 10 mD at a depth of around 2500 meters (8202 ft). Original Oil in Place (OOIP) is estimated to be 140, 900 MMSTB. The complex geology (complicated structural and stratigraphic nature of the reservoirs), lack of reservoir information and lack of technology availability caused a gap between discovery and development. Throughout a period of several decades some exploration wells were drilled based on 2D seismic and log correlations of the reservoirs. The exploitation of the Paleonchannel was postponed because most of the wells showed poor productivity. The reasons for the low recovery (around 3%) have never been thoroughly understood. Various hypotheses have been proposed to explain the deficient performance such as partial closing of the fractures with declining reservoir pressure (bubble-point pressure is near initial pressure), inadequate comprehension of the geological model, deficiency in the fracturing technology, oil-wetted or intermediate-wetted reservoirs, applicability of unconventional wells (horizontal wells, casing drilling technology), etc. Today, the Chicontepec Paleochannel is an intermediate stage. Due to the experience of different fields with similar characteristics, this paper describes an analysis of alternatives that may be considered to resolve the problems of exploitation at the Chicontepec field. Advanced technologies, hydraulic fractures, artificial lift systems, all of them combined with secondary and enhanced oil recovery, may be feasible to sustain or increase production. A number of hurdles will have to be overcome. This field, the second most important oil field in Mexico, should take advantage of the experience learned from these analogous reservoirs. Chicontepec Paleochannel Geographically, it is located in east-central Mexico in parts of the states of Veracruz, Puebla and Hidalgo. Chincontepec system was deposited under complex tectono-stratigraphic conditions. Geologically, it covers an area of 957,534 acres (Figure 1). Aproximately half of Chicontepec consists of shales or silty shales with the rest of the formation made up of multiple thin sandstones beds and zones of sandstones beds. Typically, between 8 and 16 major reservoirs are present. These set of reservoirs is composed of channel complexes that are flanked by, and rest on, lobe sandstones that grade into distal fan and basin floor deposits, resulting in high heterogeneity. Throughout a period of several decades some exploration wells were drilled based on 2D seismic and log correlations of the reservoirs. The 3D seismic allowed the identification of sand bodies with viable pay thickness. Some wells produce small amounts of water, in general, water-oil contacts have not been identified. X-ray diffraction analysis showed that the clay cointains dominantly kaolinite with a content of 1 to 5 %. The sandstones are immature litharenites consisting of quartz grains, abundant carbonate fragments, and granitic fragments. Because of the abundance of carbonate in the system, the sediments are highly cemented by ferroan calcite and ferroan dolomite, in addition to quartz overgrowths. Core analyses show that the reservoirs are characterized by both low porosity and low permeability, Figure 2. All the reservoirs have permeabilities of 0.1 to 10 mD and porosities ranging from 5 to 15 %. The effective permeability, as determined from build up, fall off, drawdown and step rate test or advance decline analysis, varies from 0.01 to 15 mD.