Overview of Tight Gas Reserve in Northern Arabian Gulf
While conventional natural gas streams from the earth relatively easily, unconventional gas finds are more difficult to develop and more costly to produce. As technologies and skills improve, unconventional gas is a variable concept because some finds may become more easily or economically produced over time, no longer making them unconventional. Right now, there are six main types of unconventional gas, including deep gas, gas-containing shales, coalbed methane, geopressurized zones, Arctic and subsea hydrates, and tight gas.
Tight gas is natural gas that trapped in very low permeability reservoir rocks that massive hydraulic fracturing is needed to produce the well at economic rates. Tight gas reservoir generally has less than 0.1 milidarcy (mD) matrix permeability and less than 10% matrix porosity. The tight gas reservoirs exist mainly in the Paleozoic sequence at depths greater than 10,000 feet. These reservoirs consist mainly of clastic rocks and range in age from Cambrian to Permian. The permeabilities of sands in Saudi Arabia are between 0.01-0.08 mD and the porosities are 4-6%. Tight gas exploitation is needed to fulfill the gas demands for natural gas. For the production process, a large scale of hydraulic fracturing is needed, tight gas reservoir also will be applied to one of modern drilling technology that can help produce gas from tight reservoirs of drilling multilateral wells. Tight gas is produced when sandstone is being pressured by the rocks above it that caused diminution of the pores so the gas under the sandstones was trapped.
One of the area in Saudi Arabia that has potential of tight gas is Rub-Al Khali area because this area is full of sandstone that could possibly be the tight gas reservoir. Rub-Al Khali is largest sand dessert in the world. By studying the regional geology of Saudi Arabia, knowing the characteristics of sandstone in Saudi Arabia and the age of the sandstone, Saudi Arabia could be expected as one of the most potential tight gas reservoirs area. Saudi Arabia has 2549 Tcf reserves of natural gas. Most tight gas formations are found onshore, and land seismic techniques are undergoing transformations to better map out where drilling and development of these unconventional plays. Typical land seismic techniques include exploding dynamite and vibroseis, or measuring vibrations produced by purpose-built trucks. While these techniques can produce informational surveys, advancements in marine seismic technologies are now being applied to land seismic surveys, enhancing the information available about the world below. Not only providing operators with the best locations for drilling wells into tight gas formations, extensive seismic surveys can help drilling engineers determine where and to what extent drilling directions should be deviated. While vertical wells may be easier and less expensive to drill, they are not the most conducive to developing tight gas. In a tight gas formation, it is important to expose as much of the reservoir as possible, making horizontal and directional drilling a must. Here, the well can run along the formation, opening up more opportunities for the natural gas to enter the wellbore. A common technique for developing tight gas reserves includes drilling more wells. The formation is tapped, the more the gas will be able to escape the formation. This can be achieved through drilling myriad directional wells from one location, lessening the operator's footprint and lowering costs.
AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015