The Development Technology of Non-homogeneous and Multilayer Sandstone Reserve in Daqing Oilfield
Authors: Jianwen Yan , Dang Huilan , Tian xiaochuan , Ding Haitao , Wang Hongtao 
Published: December 2007

Abstract
This paper introduces the present development situation and the technologies for improving the recovery ratio, describes the development states of pay zones in super high water cut stage, the distribution characters of remaining oil and the issues that face the advancing development, and presents the outlook of the oilfield.

Introduction
The total water cut of the La-Sa-Xing reservoirs in the Daqing Oilfield has reached 90%, which is extremely high for a water flooding oilfield. The residual oil distribution scatters and it is difficult to recognize it clearly. Most of the thicker zones have been put into production and other layers are highly scattered, thin, sand-and-mud overlapping as well as non-homogeneous layers with different crude properties and complex pore structures. It is quite a challenge to discover this part of the reservoir. How to determine these oil areas? How to divide the thin layers with low permeability? How to avoid the channeling between thin interlayers during the process of well cementing? These problems are quite difficult in oil fields development. But it is significant to tap the latent power of thin and low permeability layers to improve the final recovery of the La-Sa-Xing reservoir in the Daqing Oilfield. In that case, the finite geology study was made which developed the completion and economic evaluation of single sand body injection-production relationship, studied the multi-science reservoir technology, logging interpretation techniques of thin and bad reservoirs, and on the basis of the above work, a series of technologies were developed including oil and gas well reservoir protection technology in drilling and cementing, high quality cementing technology, balanced fracturing technology and bridge fracturing technology which give a strong support for thin and bad reservoir's better development in super high water cut phase.

1. The present situation of oilfield development
The La-Sa-Xing reservoir in the Daqing Oilfield is a large continental facies oilfield with fluvial deltaic deposition. There are 9 oil pay zones subdivided from 3 sets of reservoirs-Sa, Pu and Gao. The reservoirs are severely heterogeneous and bear complex distribution of oil and water. The layer-internal, interlayer and planar differences of oil distribution and development are conspicuous. Since 1960 the oilfield has gone through 5 stages of development with basic well pattern, first round infilled well pattern, second round infilled well pattern, third round infilled well pattern and polymer flooding. The geological reserve that is put into production is 306.8×108bbl and the recoverable reserve is 156.5×108 bbl. There are 41437 wells at present. The reserve production rate is 0.95%, the cumulative oil production is 125.0×108 bbl and the current recovery ratio is 40.9%. The water cut of water flooding reserve is 90.15%.
Aiming at improving the recovery and development efficiency and according to the requirements at different stage, a series of technology for water flooding development has been developed and applied, the main ones of which include fine reservoir characterization, remaining oil prediction, infilled well pattern, injection-production relationship change and enhanced separate-layer water injection.

2. The technologies for improving the recovery rate

(1) Technology of fine reservoir characterization
Since the La-Sa-Xing reservoirs were developed, the geology research went through four stages comparison on sedimentary cycle and reservoir classified control, subdividing sedimentary facies, untabulted layers research and fine reservoir characterization.
The geometrical shapes and interior construction structures of sand bodies were characterized and then the geological reservoir models were built up based on the study of deposition characters and depositional interfaces from logging data in dense well patterns and the sediment laws and the sedimentation models. Using graded analysis and mode-predicting description methods, the heterogeneous systems of the reservoirs were described systematically.