The present invention is a new low-cost method of boosting the pressure of a gas from a lower level to a higher level, for any purpose, one of which may be to inject the gas into a higher-pressure receptacle for purposes of sale, or to carry out some mechanical function. More particularly, it relates to such method and system especially adapted to the economics of the equipment used to increase the pressure (to pressurize or compress) the gas from a marginally-profitable gas well to a level acceptable for insertion into a gas sales line.
The present invention relates to a new low-cost method of compressing natural gas from a gas well when the reservoir pressure of the producing zone has declined below the pressure of the gas sales line. The present invention takes low-cost standard oil-field equipment and combines them into a unit that will compress gas more economically than a conventional compressor. The present invention relates, specifically, to the use of a flexible bladder inside a steel vessel, to receive and temporarily store natural gas from a gas well. In order to increase the pressure of the temporarily-stored gas inside the bladder, a hydraulic fluid is pumped into the annulus between the outer walls of the bladder and the inner walls of the steel vessel. With continued pumping, the pressure of the hydraulic fluid will exceed the gas pressure inside the bladder and the bladder collapses in size which results in the gas inside the reduced-size container (the bladder) being elevated to a higher pressure. The higher-pressured gas is then transferred to a natural gas pipeline for sale, or to some other mechanical process served by the higher-pressured gas. In the absence of an indirect method of pressurizing the gas, a more-expensive mechanical compressor would have to be used which would increase the cost of recovering the natural gas and result in natural gas reserves being abandoned which could be recovered by using the less-costly indirect compressor.
The present invention is specifically-related to the recovery of economic gas reserves when well-head pressures decline below the minimum suction pressure for conventional mechanical compressors, however, other uses of the equipment may be to collect small amounts of gas produced with oil for which there is no gas pipeline connection, to pressurize it into storage and further pressurize it for disposition by truck transport to a pipeline. Other uses may be to pressurize low-pressure gas from a local utility pipeline (approx. 1 psig) to 1000-1500 psi for compressed natural gas (CNG) fuel in isolated areas.
The flexible bladder is a one-piece cylinder-liner, when filled with gas from a gas well, or other source of low-pressure gas, will inflate substantially to the interior walls of the steel cylinder. The steel cylinder is sized to accommodate a number of fill-empty cycles during a 24 hour period such that the total volume of gas processed in a 24 hour period is substantial and the revenues generated from the sale of such gas will return the investment therein in a short time. The bladder is made of rubberized nylon, or if by choice, some other member of the elastomer family of synthetic rubbers, compatible with natural gas, and certain other gases, and a hydraulic fluid composed of fresh water -antifreeze mix, or mineral hydraulic oil, sealed at one end and the other end open and attached (bonded) to the face of a flange attached to the steel cylinder for pressure containment.
The hydraulic fluid is a matter of choice and can be either a water-antifreeze mix or hydraulic mineral oil.
In the method and system of the invention, an Indirect Pressurization Facility (IPF), consists of gas loading and unloading conduits, gas control mechanisms, pressure and temperature measurement devices, a bladder-equipped steel cylinder pressurization unit and a hydraulic system (pump, prime mover and surge-reservoir tank). The prime mover will be a gas engine and the pressurizer will be a centrifugal pump. Fuel for the prime mover will be natural gas from the gas well or other supply.
Start-up operations will commence with an xe2x80x9con-offxe2x80x9d switch, when placed in the xe2x80x9conxe2x80x9d position will enable the control panel to signal the valve on the gas supply line to open and gas to flow to the suction of the indirect pressurization facility, and from there to the interior of the bladder. When the amount of gas necessary to fill the bladder is confirmed by a sensor, the fill valve will close and a signal sent to the pressure pump on the hydraulic system to pump hydraulic fluid into the annulus between the outside of the bladder and the interior of the pressurization chamber. When the annulus pressure reaches the pre-set discharge pressure, pumping into the annulus will be discontinued. At this point, the bladder will have collapsed which will compress the gas trapped inside the bladder after which the pressurized gas will be transferred to the gas sales line, or to storage. Following discharge of the gas to sales, the pressurization chamber is de-pressurized by opening the annulus to a reservoir located beneath the steel cylinder which will receive all of the fluid from the annulus at atmospheric pressure and supply the fluid to the suction of the centrifugal pump to pressurize it to the maximum working pressure of the pump and have it ready to commence the next pressurization cycle as soon as the bladder fills with gas from the supply well. The cycle is then repeated as long as the gas well has sufficient producing capacity to load the bladder at atmospheric pressure.