Microseepage of methane to the atmosphere from the Dawanqi oil‐gas field, Tarim Basin, China

Abstract

The microseepage of natural gas from subsurface hydrocarbon reservoirs is a widespread process in petroleum basins. On a global scale, microseepage represents an important natural source of atmospheric methane (CH4). To date, microseepage CH4 flux data have been obtained from ~20 petroleum systems in North America, Europe, and Asia. While the seasonal variations of gas flux due to soil methanotrophic activity are known, the role of geological factors in controlling gas fluxes has been poorly investigated. Here we present new microseepage data from the Dawanqi oil‐gas field located within the Tarim Basin (China), a petroleum system characterized by intense faulting and shallow (<700 m) reservoirs. We measured CH4 fluxes from the ground at 51 sites along three transects by using a closed‐chamber connected to a portable gas sensor using off‐axis integrated cavity output spectroscopy. Our results indicate that the highest CH4 fluxes occur over faults and/or shallow reservoirs, especially those that were not developed and that have higher fluid pressures. Microseeping CH4 is thermogenic, like that occurring within the Dawanqi reservoirs, as demonstrated by 13C enrichment (δ13C from −46.3‰ to −30.7‰) in the chamber. Mean and range microseepage values (17 mg m−2d−1; from −1.4 to 330 mg m−2d−1) are similar to those reported for other petroleum fields with active tectonics. Our results confirm that dry soil over petroleum fields can be a net source of atmospheric CH4 and its flux is primarily controlled by faulting, and reservoir depth and pressure. These factors shall be considered in global bottom‐up seepage emission estimates.

Methane in Soil Gas and Its Migration to the Atmosphere in the Dawanqi Oilfield, Tarim Basin, China

“…The microseepage database of Etiope and Klusman [26] shows that, statistically, positive fluxes occur in less than 50% of a petroleum field's area, and there are three possible levels of microseepage. Based on this, total methane emissions to the atmosphere in the Dawanqi field were evaluated be on the order of 60 t/yr [27]. Negative fluxes are a consequence of methanotrophic activity when the speed of diffusion and infiltration of methane from the oil reservoir is lower than that of its methanotrophic oxidation activity.…”

Faults as Windows to Monitor Gas Seepage: Application to CO2 Sequestration and CO2-EOR

“…One of these has been adapted to and coupled with a flux chamber. Tang et al [35] reported CH 4 seepage measurements using this instrument at the Dawanqi and Yakela oil fields. This will result in a substantial increase in speed and sensitivity of flux measurements.…”

Investigating methane emissions from geologic microseepage in Western New York State, United States

“…The previously published global microseepage data set contains 1,509 measurements from 10 hydrocarbon basins (Table 3; Klusman et al, 2000;Klusman, 2003;Etiope, 2005;Klusman, 2005;Etiope et al, 2006;LT Environmental, 2007;Tang et al, 2007;Etiope & Klusman, 2010;Tang et al, 2010Tang et al, , 2017. Sampled areas are primarily in Western United States, Italy, and Northwest China, with a few additional measurements in Romania and Greece, leaving most of the world's hydrocarbon basins unrepresented in the global data set.…”