The Pulse Water Injection Research and Application in Offshore Oilfield
Authors: Wang Yunxian , Liu Ming , Yang QingHong , Feng Xin , Zhou Tiyao , Wang Lirong , Li Tingli , Zhang Jianmin , Zhang Lan , Hu Yong , Zhai Guangfu , Liu Peng , Li Fenghui 
Published: March 2015

Abstract
In this paper, the pulse water injection, one of green and cheap EOR techniques, is achieved by simply changing the water injection intensity and sequence. The factor sensitive analysis is made by 2-D&3-D reservoir mechanism simulation model. Based on the mechanism simulation model, the influence factors of pulse water injection are studied.
BoZhong 25-1S (BZ25-1S) Oilfield located at Bohai Bay of China is a typical channel sandstone reservoir with banded sand distribution, severe planar and inter-layer heterogeneities. According to the pulse water injection mechanism research achievements and method of oil reservoir physics, the field-test factors like start time, injection intensity and injection cycle are optimized by the BZ25-1S Oilfield geological simulation model. Field-test project is made just for a pilot group in BZ25-1S Oilfield.
The field-test result shows that the study work flow of the pulse water injection is correct and with the sequence of pulse cycle increasing, the oil increased in every cycle will decline. The field-test research draws the conclusion that pulse water injection could improve the development effects after the field application in BZ25-1S Oilfield.

Introduction
BoZhong 25-1 South (BZ25-1S) Oilfield located at Bohai Bay of China is a first developed fluvial-dominated sandstone heavy oil field deposited in shallow water deltaic environment and one of the most complex tertiary fluvial fields. The reservoirs in BZ25-1S are small and complex fluvial channels with complicated geometry. The seismically detected channel size ranges from 100–300m wide and 500m to several kilometers long. Those channels were formed at different geological times. They cross-cut each other resulting in severe planar and inter-layer heterogeneities and many geometrically complicated reservoir systems(Figure 1). The small and geometrically complex channels result in poor reservoir connectivity(Figure 2). Porosity ranges from 20% to 40%(average 30%). Oil density (surface) is about 0.94–0.96 kg/m3, with viscosity (under reservoir conditions) of 20–250 cp.
The oilfield is developed by irregular well patterns with well space of 300–400m. Vertical/deviated and horizontal wells were used to develop this reservoir(Figure 3). Each vertical/deviated well usually penetrates multiple sand layers with thickness of each sand layer ranging from &lt;0.5m to &gt;10m. The averaged total sand thickness encountered by a vertical/deviated well is about 21m. Horizontal wells were mainly dedicated to large single sand channels.

Field Production Performance
Early production from August 2004(first oil) showed steep pressure and production decline(Figure 4 & 5). Quick implementation of water injection on August 2005 arrested the fast production decline and stabilized reservoir pressure. However, the severe planar and inter-layer heterogeneities result in inefficient vertical or horizontal sweep efficiency in individual regions.