There are many oil and gas conventional reservoirs in Saudi Arabia have been exploited, but still there are also need to be explored and produced especially in the fields of unconventional shale gas. Investigation the extending of rock source of the hot shale gas Qusaiba formation in North part of Saudi Arabia, the most important rock source in the word, is crucial for one of the most promising shallow shale gas reservoir in the region. Most previous studies in the area were a geological, petrographical, petrophysical, geochemical characteristics or well logs studies which are not enough to show the continuously of the reservoir and map the diverse of the depth changes. The lack of the geophysical studies in the area inspiring to perform such study and image how the continuously and behavior of the reservoir subsurface. Imaging the geological stratigraphy of area utilizing a multiple geophysical methods is a crucial step to disclosure the unconventional reservoir and understand the source rock extending underneath the North region of Saudi Arabia. A good achievement is shown in this study using this integration of seismic migrated image and gravity geological model. This integration provides a robust and true subsurface geological formations, structures, and determined thickness and depth of the Lower Silurian Sharawra Qusaiba and Sarah formations. This work would be a valuable contribution in unconventional reservoirs exploration in shale gas in Saudi Arabia.
Shale gas plays a main role in the recent hydrocarbons exploration industry. North part of Saudi Arabia is one of the most promising unconventional gas reserves in shale gas reservoir geologically and known by Qusaiba Formation. The Qalibah Group is located in this part of the Arabian shield and consists of two Formations: the (upper) Silurian Sharawra Formation and the (lower) Qusaiba shale Formation. Silurian Sharawra consists mainly of sandstone and siltstone with beds of shale. The important of Silurian Sharawra is that it is laying over one the biggest rock source of hydrocarbon in the region Qusaiba Formation. The Formation is presented from outcrop exposures in subsurface in this part of Saudi Arabia [
To explore the unconventional shale gas many studies and field works were conducted in several locations in Saudi Aribia. One of the interesting studies on unconventional shale gas was done in North West of Saudi Arabia to investigate pore pressure prediction for the hot shale of the Qusaiba formation and Sarah Formation using multi well logs data in the area supported with 3D seismic data [
Here, we aim to utilize the integration of high resolution reflection seismic and gravity data to image the sequence of subsurface layers and structures of near surface shale gas formations and verify of the reservoir characterization depth and thickness for unconventional gas fields exploration and production in the region.
In Tayma area in Saudi North part, determining the rock source Qusaiba Formation and detecting the top depth of the Formation will be most beneficial to verify the depth of hot shale gas and mitigate the uncertainties of source rock Surillian Qusaiba and Sarah Formation
and South Arch host of oil and gas.
Using the seismic imaging was so critical because the Qusaiba shale in North West is very shallow comparing to its depths in Central and South part. In this study, 2D seismic profile was acquired using 96 channel and 408 shots. The intervals of sources and receivers were 10m with the minimum and maximum offsets 5 m and 950 m, respectively. We utilize one Mini IVI Vibrosies source to shot 408 linear upsweep with bandwidth between 20 - 200 Hz and stacking 3 numbers of sweeps. The field Parameters were selected based on testing shots that showed the best parameters for the nature geological phenomena and area accessibility. The layout of seismic survey in study area was spreading on the top of Sharawra shale layer. It was suggested to have the seismic survey on the surrefce of Qa Buhan, but the idea changes because of some field observations
structures. In the gravity interval, recording locations were identical with the seismic survey and exactly over the locations of the seismic source shots.
Commonly, Shale is heterogeneous and brittleness undersurface. The surface Sharawra formation is mainly composed of sandstone with many beds siltstone and shale. The strength of our source (Mini IVI Vibrosies source) is prop for near surface application but according to the lithology of the subsurface, we recognized absence of some high frequencies underneath and appear a wide of the ringing waves. These ringing and discontinuous horizons may refer to the lithology diversity between litstone and sandstone beds and brittleness shales layers inside Sharawra Formation in shallow part, which are marked by the red square in seismic section
In
shale” (TOQF) and Sarah formation (TOSF) with some interactions of shallow geological structures and faults appearing in the middle of the section. According to high frequencies signals attenuation caused by sandstone surrounding Sharawra shale beds with lower and upper huge amplitude energy were loose and caused absent of the deep formation beneath the Sarah formation.
Gravity data was acquired along the seismic line with 4100 m length and interval 100 m between stations to detect and map an unexplored lower Silrurian Qusaiba-Plaeozoic Formation.
Therefore, the gravity geological model seems longer the seismic data
Mapping the subsurface of organic-rich shale gas of the Lower Silurian Qusaiba formation and Sarah formation are performed using the integration of seismic and gravity data. The investigation of the unconventional Qusaiba hot shale reservoir in North of Saudi Arabia is necessary to increase the possibilities of exploring the shale gas field in the area and to decrease the uncertainties of subsurface depth and thickness of the rock source. Imaging of the migrated 2D seismic data and modeling of 2D profile gravity data are performed in order to distinguish the subsurface formations and detect their depths and thicknesses. The present integration modeling and imaging results are showing identical
detections of three formations: Sharawra (on surface) followed by Qusaiba and Sarah formations. The depth of the shale gas Qusaiba formation is diverse and the continuously is interpret with some shallow geological faults. The result of migrated seismic prove the laying of Sharawra formation on the surface which is ascertained as well by the field surface scenes and evidences of the outcrop. The lithology of the Sharawra formation exhibition with a series of sandstone interfering with thin interbed shale along the Formation cause a wide of multiple ringing in shallow seismic waves. The work result adds a respected contribution in shale gas unconventional reservoir exploration and development in North part of the Saudi Arabia, but it needs more data for verification and covered field works to discover the area significantly. Moreover, it is highly important to increase the income profits for Saudi Arabia in shale gas.
The author would like to acknowledge King Abdulaziz City for Science and Technology for supporting this work. Many thanks shall extend the geophysical team of KACST for conducting some activities related to this study.
Alajmi, M., Alotaibi, A., Aboud, E., Alharbi, A. and Almalki, M. (2018) Observations “Detections” of Shallow Unconventional Qusaiba Shale Gas Reservoirs North Part of Saudi Arabia. Journal of Geoscience and Environment Protection, 6, 257-265. https://doi.org/10.4236/gep.2018.65022