Abstract
In the fall of 2016, a field study was conducted in the Uinta Basin Utah to improve information on oil and natural gas well pad pneumatic controllers (PCs). A total of 80 PC systems at five oil sites (supporting six wells) and three gas sites (supporting 12 wells) were surveyed, and emissions data were produced using a combination of measurements and engineering emission estimates. Ninety-six percent of the PCs surveyed were low actuation frequency intermittent vent type. The overall whole gas emission rate for the study was estimated at 0.36 scf/h with the majority of emissions occurring from three continuous vent PCs (1.0 scf/h average) and eleven (14%) malfunctioning intermittent vent PC systems (1.6 scf/h average). Oil sites employed, on average 10.3 PC systems per well compared to 1.5 for gas sites. Oil and gas sites had group average PC emission rates of 0.28 scf/h and 0.67 scf/h, respectively, with this difference due in part to site selection procedures. The PC system types encountered, the engineering emissions estimate approach, and comparisons to measurements are described. Survey methods included identification of malfunctioning PC systems and emission measurements with augmented high volume sampling and installed mass flow meters, each providing a somewhat different picture of emissions that are elucidated through example cases.
Highlights
Oil and natural gas (ONG) well pad operations employ natural gas (NG)-driven pneumatic controllers (PCs) for production process control and safety functions [1]
In two cases (Kimray 312 FGT back pressure (BP) vessel pressure relief safety PCs on Oil Sites 1 and 2), a 12 hr process upset vent of 27.7 scf/h, once per month was assumed, with the level based on an actuation trial that simulated a process upset condition (SF1 Data1) [7]
Using the combined measurement and emission estimates (EEEs) analysis approach, the study mean whole gas PC system emission rate was estimated at 0.36 scf/h (0.33 scf/h methane), with a median of 0.11 scf/h, and a standard deviation of 0.77 scf/h
Summary
Oil and natural gas (ONG) well pad operations employ natural gas (NG)-driven pneumatic controllers (PCs) for production process control and safety functions [1]. As part of regular operations, typical well pad PCs are designed to emit a small quantity of NG to the atmosphere. Because of the large numbers of PCs in use, methane (CH4) emissions associated with this source category contribute significantly to total greenhouse gas (GHG) emissions for the ONG sector. Pneumatic devices, including PCs, account for well over 30 percent of methane emissions, making them among the largest source categories in ONG production field operations [2]. Since the emitted field NG contains a small percentage of higher chain hydrocarbons, PCs contribute to volatile organic compound (VOC) emissions for the sector. To support environmentally responsible development of these U.S energy assets, it is of ongoing importance to continually improve information on the number, type, operational conditions, and emissions of well pad PCs, as well as methods to characterize these emissions
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