Diagenesis and Reservoir Characterization of the Block V-Lamar Field, Maracaibo Basin, Venezuela

GONZALES, CESAR and FLORES GUSTAVO, INTEVEP, SA., Caracas, Venezuela

The Block V-Lamar field, located in the central portion of Maracaibo basin, Venezuela, Is the subject of this study. The sedimentary section corresponds to a section of the Misoa Formation of early to middle Eocene age. These sediments were deposited in the upper delta plain as stacked distributary channel bars and associated facies and consist of relatively clean sandstones, fine to medium grained, with a sublitharenitic to subarkosic composition. The clay mineral assemblage is mainly composed of kaolinite, followed by chlorite and subordinate amounts of discrete smectite, discrete illite, and mixed-layer illite/ smectite with order stratification with 20-30% of expandable layers, all of diagenetic origin. Even though there is a remnant of primary porosity reduced by silica cement, m st porosity is secondary as a result of cement, matrix, and unstable grain dissolution. The petrographic XRD and SEM data obtained allow us to define the following paragenetic sequences: (1) mechanical compaction; (2) silica cementation; (3) patchy calcite cementation; (4) Dissolution of matrix, cements, feldspars, and rock fragments; (5) kaolinite precipitation at or near feldspar intragranular pores; (6) matrix recrystallization to chlorite; (7) precipitation of second generation of kaolinite; and (8) precipitation of smectite. The porosity and permeability distribution in the reservoirs is the result of the net effect of the different diagenetic events that include early diagenesis, medium to late diagenesis, and telodiagenesis, mainly in response to basinwide tectonism.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)