Low Frequency Passive Seismic survey, also called Infrasonic Passive Differential Spectroscopy (IPDS), is a unique technology for hydrocarbon reservoir detection and monitoring from the surface. The technique is based on the principles of non-linear behaviour of multiphase fluid systems in porous reservoirs. It is well-known that the relative compressibility of Hydrocarbon fluids (gas & oil) is higher than water. Therefore, the Hydrocarbons fluid in the pore system can be detected at the surface as a characteristic alteration of the normal signature of the natural earth’s noise signal movement in the low frequency range between 1 Hz and 10 Hz (Figures 1 & 2), which can be measured by very high sensitive hydrocarbon sensor. The nonlinear spectral signature of hydrocarbon bearing reservoirs behaviour is different than the water bearing reservoirs (Figure 3).
The technology is based on high success ratio drilling results and it is gaining a lot of momentum in the petroleum industry, and its potential in exploration areas, discovery delineations, and developed fields is now being recognized. The Reservoir Hydrocarbon Indication (RHI) technology was applied in many countries worldwide since 1996 with over 30,000 measurements covering numerous exploration (Hydrocarbon discoveries and dry locations) and production (appraisal, producer and injector) wells. Over 130 survey campaigns were acquired from several exploration and development areas in the Middle East (Egypt, Sudan, Ethiopia, Nigeria, UAE, Kuwait, Jordan & Saudi Arabia), USA, Russia, Europe others, most of these surveys were successful completed during the last 17 years.
The main objective of the Passive Seismic survey campaigns was to run such surveys as exploration, delineation, reservoir monitoring and time laps monitoring tool under any kind of geographic conditions or with any type of geological system, structure, stratigraphic and lithology (sandstone, limestone, igneous, salt, anhydrite, etc.) it will have no effect on low frequency anomalies. However, the main effect is to determine whether hydrocarbons exist or not in porous media. The secondary objective was to provide information concerning detailed lateral and vertical hydrocarbon distributions away from well control points (quantity and quality), and more recent studies are being conducted to develop the technology for addressing the detection of hydrocarbons depth and possibly the staking pattern of the reservoirs.
Results available with GeoDynamics WorldWide and other associates are very encouraging. The key finding is that the correlation between hydrocarbon pay zone thicknesses (gross or net pay) and Reservoir Hydrocarbon Indications (RHI) data is high, often in the order of 80%, both for exploration wells, undeveloped fields and producing fields (Figures 4, 5 & 6).
A number of blind test wells were drilled and over 80% of them produced results in line with the RHI predictions, strongly supporting the technology, and it had highly reduced the drilling risk and minimized the time and uncertainties.
The Passive Seismic (RHI) technology therefore appears to be very promising.
Recently, there is significant demand for the passive seismic low frequency surveys for reservoir hydrocarbon indicator (RHI), and also for passive seismic high frequency to monitor micro-seismic and detect the fractures activities and distribution.
Currently, GeoDynamics WorldWide & Tanqeeb have several potential projects in the Egyptian petroleum sector with government and private companies.
By Karim Akrawi (PhD), GWW Managing Director – Tamer Fareed, Tanqeeb Managing Director
Figure 1: Raw signals from passive seismic sensor
Figure 2: Comparison of Reservoir Hydrocarbon Indicator (RHI) analyses in oil and in water media.
Figure 3: Comparison between oil and water Passive Seismic spectrum analyses
Figure 4: Developed oil reservoirs monitoring, the survey results confirm water front and by drilling four wells after passive seismic survey
Figure 5: The chart shows the correlation between RHI and Net Pay Zone from wells surveys
Figure 6: Data integration between 2D/3D Seismic and Passive seismic (RHI) results.