JIANYU, CHEN, GUAN ZHENLIANG*, ZHU SHUIAN, JAMAL GIUMAA ABOURGIGAH China University of Geosciences,Wuhan, China, KANG RENHUA, HUANG GAOJIAN Shengli Petroleum Administration, Dongying,China

Abstract: Integration of Geological, Geophysical and Engineering Data to Detect Compartmented Turbidite Reservoirs in the Bonan Oil Field, East China

The Bonan oil field is located near the depocenter on the southern gentle slope of the Bonan rift sub-basin in the Jiyan basin, east China. It is the biggest one both in the area and in the reserves among deep (>3000m) buried, faulted-lithologic fields in the Jiyan basin, the second largest petroliferous basin in China. The Bonan sub-basin is bounded on the southeast by the Gudao uplift and on the south by the Chenjiazhuang uplift. Both of them consist of the Paleozoic carbonate basement and Neogene clastic drape, thus providing the material source for the Paleogene deposition in the basin. The internal stratal stacking patterns within the rift basin are primarily controlled by sediment delivery systems, basin gradient and activity of syn-depositional boundary fault.

An integrated reservoir characterization has been conducted for the reservoirs in the Bonan oilfield, using 340 wireline logs, 20 well cores, 3D seismic data, high-resolution sequences study, petrophysical evaluations, production history and reservoir simulation, in order to establish an more accurate geological model and improving the reservoir management.

The reservoirs in the Third Member (Es3) of the Shahejie Formation of the Eocene are most prolific in the field and comprise multiple layers of turbidite and fandelta sandstones. The reservoir compartmentalization was caused by the pinchout of the sandbody and the impedance of surrounding lacustrine mudstone and oil shale.

High-resolution sequence stratigraphy was applied to identify the sequences of different levels and to quantify their vertical and lateral continuity.The Third Member (Es3) contains 14 sandstone units, among which the 9th unit is productive near-source turbidite accumulated in highstand system tract and is the focus of this paper.

The 9th sandstone unit deposited in the topography trough SE-NW and exists between the dark mudstone on the top and oil shale on the bottom, further is divided into 4 sand body groups, corresponding to the 5th sequence of average duration shorter than 100.000 yr. The boundaries are laterally continuous mudstones, have a low gamma ray and spontaneous potential responses, and act as important pressure barriers for the reservoirs.According to the synthetic sedimentary researches, in particular, the thickness, log configuration and extension of sandbodies, the turbidite fan of the 9th sandstone unit consists of the superposition of cyclically accumulated multiple fans, separated by the erosive base (Fig.1). Overall it has the length of 20km, the width of 6km, average sandstone thickness of 50m and extends from southeast to northwest. Individual channel fill has lenticular shape in the profile of 1000-1500 m-wide, up to 30 m-thick and shows low sinuosity and less offset.

Channel fill facies across the oilfield comprise (1) unstratified. normally-graded beds of clast-supported conglomerates, intraclastic sandstones, and coarse- to medium-grained felds-pathic sandstones with the thickness 2-5m deposited in the main channel in the inner fan (2) fine-grained sandstones of the thickness < 2m with intercalated mudstone deposited in the channel-levee in the inner fan (3) medium- to fine-grained feldspathic sandstones of the thickness 3-10m with dispersed pebble-sized mud intraclasts deposited in the braided channel in.the middle fan (4) interbedded mudstones and massive (< 2 m) fine-grained feldspathic sandstone and calcareous sandstone beds as channel fringe or interchannel deposits in the middle fan.

The key factor controlling the reservoir geometry, scale and internal heterogeneity, in turn, the production and remaining oil of different sandbodies is sedimentary micro-facies and diagenesis. The extensive braided channel sandbodies in the middle fan facies are the most important reservoirs in the Bonan oilfield.

Due to the nearby source, lithologically 9th sandstone units are characterized by low mature composition, poorly sorted and grounded.The strong compaction at great depth (3100-3400m), quartz overgrowth and clay minerals slugging result in low porosity (10-20%) and low-permeability(0.1-50*10-3½¡m2), as well as poor connectivity (Fig.2). The total oil production of the Bonan oilfield reached the peak of 1.87 million ton in 1989, afterwards, the yield drops at a ratio of 17.5% per year and waterflood quickly widespreads. The development data display that the highly productive wells are located in the channel facies and also the waterflood progrades mainly along the channel sand body.The precise characterization of the turbidite reservoir is very interesting for recently increased exploration and development activities at great depth in the rift basins in east China.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England