(1) acquisition parameter analysis
Because there is no drilling in deep water area, there are few seismic data and poor quality, and there are many uncertainties in its strata, trap implementation and reservoir-forming combination. Therefore, the main purpose of seismic data acquisition and design of deep-water long cable is to implement structural and lithologic traps and sag structures and evaluate hydrocarbon sources and reservoir conditions.
On the basis of analyzing the existing seismic data, the range of seismic effective frequency band is determined according to the needs of exploration. At present, the purpose of deep-water seismic exploration is to carry out structural trap, depression determination and hydrocarbon source evaluation, and initially draw up the resolution of 30m in Lingshui Formation, which requires an effective source bandwidth of 6 ~ 6~ 100Hz. At the same time, a simple geological model is established according to the existing seismic data and understanding, and the acquisition parameters are analyzed on this basis. Through analysis, the seismic data acquisition parameters are finally determined as follows (Table 5- 1):
Table 5- 1 Acquisition Parameter Table
(II) Configuration of seismic acquisition equipment
The towing of the whole underwater equipment is completed by a single ship, and the acquisition operation is undertaken by Nanhai 502 ship, which uses Syntron RDA cable with a length of 7500m and 600 channels. The focal capacity is 3680cu.in, which consists of four subarrays. The cable sinking depth is 6m, and the source sinking depth is 5m. The main equipment used in acquisition construction is as follows (Table 5-2).
Table 5-2 List of Purchasing Construction Equipment
Syntrak960 digital seismic acquisition system consists of multi-cable seismic signal receiving processor (MSTP), multi-cable recording system (MSRS), system controller, quality control monitoring system and cable tension monitoring system. Multi-cable seismic signal receiving processor (MSTP) is a bridge connecting cable system and recording system, and also a tool for setting acquisition parameters and cable configuration. Multi-cable recording system (MSRS) receives the data collected by MSTP and sends them to tape drive for recording and plotter drawing respectively. The system controller is an industrial computer, which controls the activities of MSTP and MSRS through high-speed serial data lines. QC monitoring system is a graphic workstation based on Windows3. 1 1. It is connected with QCGⅱ board (installed in MSTP cabinet) through two 55MB/S high-speed serial data lines, and the seismic data collected by the cable are displayed on the high-resolution graphic display in real time. At the same time, the system can also analyze the root mean square noise energy of the collected data.
Nanhai 502 is now using RDA cable produced by Syntron Company, which can effectively reduce the cable resistance and noise, and can bear the towing force of 12000m long cable at most. The track spacing of the cable can be set to12.5m,18.75m or 25m through the program plug-in. This project adopts12.5m track spacing.
Spectra integrated navigation system is a real-time navigation system based on UNIX operating system developed by British Concept System Co., Ltd., which is used for multi-cable multi-source 3D seismic exploration and single-cable single-source 2D seismic exploration. The system is mainly used for the control of construction operation parameters and network parameters, shot point budget and blasting control, collection and recording of original data, and real-time monitoring of sensor data and network quality. At present, the software version used by Nanhai 502 ship is 9.8.04.
GCS90 seismic source system is manufactured by SYNTRON, which can control up to 96 air guns at the same time. It consists of gun controller, multiple ignition power sources (one ignition power source is required for every 16 gun), display and printer. Nanhai 502 ship is now equipped with four power sources, which can control up to 64 guns.