Reservoir
Characterization of Lacustrine Argillaceous Dolomite with Trona Interbeds
Yao, Guangqing1, Fengde Zhou2,
Timothy R. Carr3, Shangru Sun4 (1) China University of
Geosciences, Wuhan,Hubei, China (2) China University of Geosciences, Wuhan,
China (3) Kansas Geological Survey, University of Kansas, Lawrence, KS (4)
Henan oilfield company , Sinopec, Nanyang, China
In the center of Tertiary lake-basin
within the Biyang depression of the Henan Province, central China, a suite of thick
dolomitic units totaling more than 1500 meters was deposited by a perennial
alkalescence saline depositional system (Hetaoyuan Formation). The lithic
succession of shale (mudstone)-dolomitic marlstone - argillaceous dolomite-
dolomite –trona records the procession from freshwater to increasingly salty
water. In subsurface high quality trona ore was developed for commercial
purposes. Reservoir whole-core data indicate fracturing and dissolution is
present in the reservoirs. However, until this study, the dolomite reservoir quality
and the potential were unclear. This study uses integrative techniques to
characterize the dolomite reservoir. Available techniques and methods include
analysis of sedimentary facies, high-resolution sequence stratigraphy,
diagenesis and stress field. Fifteen short-term cycles are divided in sections
and provide the basis to construct a rhythm-cycle record model of the dolomitic
series. Detailed sections and sub-surface facies maps provide reliable indices
of reservoir properties and the distribution of trona layers. Associated with
the fractures, dolomite dissolution is identified through core and log
analysis. The size of secondary pore space ranges from millimeter to centimeter
scale. Based on well-bore deformation, rock acoustic emission testing, structural
surface curvature analysis and simulation of the distribution and density of
potential fracture system, the ancient maximum stress direction is
northeast-southwest. Results indicate the dolomite units of the Hetaoyuan
Formation have the potential for oil and gas accumulation with good reservoir
quality resulting from a dual system of fracture and dissolution porosity.