Primary Drive Mechanisms Primary drive mechanisms basically recover hydrocarbons from the reservoir using the natural energy of the reservoir, without the need for any external energy. Primary drive mechanisms will directly or indirectly decrease reservoir pressure or, in other words, cause pressure depletion.Solution Gas DriveSolution Gas Drive is classified as petroleum reservoirs that initially do not contain free gas but instead develop gas free upon exhaustion of pressure and this operation requires the reservoir rock to be completely surrounded by impervious barriers. This push comes into action when the pressure drops below the bubble point and the expansion and exsolution of dissolved gases becomes the main source of energy. Other forms of energy can come from the expansion of rock and water. This type of reservoir is said to be undersaturated or saturated, so if it is undersaturated, the reservoir pressure is greater than the bubble point pressure and vice versa for the saturated condition. If it is an undersaturated reservoir, there will be no free gas until the reservoir pressure drops below the bubble point pressure and the energy boost occurs through expansion of the rock mass and reservoir liquids. For saturated reservoirs, oil production results from the expansion of gas bubbles caused by pressure exhaustion. The oil and water will reduce slightly, but the volume of the expelled gas and its subsequent expansion will compensate for this phenomenon. From this drive you can know information such as pressure, GOR and fluid production history. Pressure can drop significantly if the reservoir is initially undersaturated due to the fact that the compressibility of rock water and oil is lower than gas. F...... half of the paper...... of the mechanisms. Compaction Unit A reservoir is considered to be a compaction unit when pore volume contraction prominently leads to overall expansion while the reservoir is saturated. This drive is supplemented by the solution gas drive and may or may not be complemented by the water/gas cap drive. This tank performs like their non-compacted counterparts, except they exhibit improved recoveries. For example, oil recovery will be greater for a solution gas drive system where the compaction drive will act like a normal solution gas drive tank. This is due to the direct consequence of the further expansion of the rocks that actually have compaction reservoirs. Due to the additional compaction, some production occurs. For example, permeability may decrease, fractures and settlements may occur, but all problems are manageable and the compaction result is very favorable.