BZ field is located at Bohai Bay of China, it is featured with multiple complex fluvial reservoirs with small lateral extension (100-300m wide) and thin accumulation (6-12m). Many channels are isolated and poorly connected across the field. As a result of the fluvial narrowness, low reserve abundance and limited natural energy, the development of this field was tied back into the neighboring field facilities and was categorized as the marginal value field with low ROR (rate of return). This paper presents a successful implementation of the flowchart of "adjust while drilling" to tap these kinds of reservoirs during the E&P circles.
In the ODP design phase, 13 well slots were reserved for the future use. And the overall geological characteristics is predicted to be much complex.
In order to mitigate risks, identify potential opportunities and improve the benefit of plan, a work flow integrating seismic, geology, logging and productivity forecast, with exploration concepts was designed during development phase to optimize drilling schemes.
The process is divided into 5 steps: 1. Locate and characterize key sands by combined analysis of logging and seismic data. 2. Recognize hydrocarbon migration pattern, identify potential oil-bearing sands, and estimate OOIP; 3. Design well patterns and forecast productivity based on the reservoir characteristics and OOIP. 4. Optimize drilling sequence and well trajectory; evaluate reservoir potential and risks based on data from drilled wells, and then optimize future well locations. 5. Apply logging while during drilling (LWD) and Periscope to reach optimal landing point and ensure high NTG.
Modifications to the ODP mainly include: 1. Staggered line well pattern was adopted to develop single story channel. 2. A large number of horizontal wells were adopted. 3. Understanding on the relationship between production wells and injection wells were improved by placing the deviated injection wells at the multi-stored channel stacking. And the well spacing was determined based on the updated reservoir properties to warrant waterflood sweeping conformance and efficiency. 4. Newly proved potentials were targeted through remaining reserved slots.
Through this process, OOIP has increased by 108%, production well counting has risen from 19 to 32, locations of 9 wells reserved during ODP phase have been successfully optimized and redirected; independent P-I pairs have been positioned for each single story channel with the P-I ratio over 90% and good response between those pairs. Average productivity has reached 1.5 times of the designed level.
The overall successful development of BZ field has proved the effectiveness of the flowchart, which is designed for the risk mitigation, potential tapping, slot utilization and financial performance enhancement. Therefore, it provides an insightful guidance for the future similar reservoirs development program design.