On March 30, 2004 Jaime Adkins, COGCC Northwest Area Engineer received Sundry Notices from Encana Oil & Gas (USA) Inc. (“Encana”) regarding their plans for remedial cementing of two recently drilled gas wells, the Schwartz 2-15B and the Brown 11-2C. These wells are located, respectively, in Sections 2 and 11 of Township 7 South, Range 92 West. Mr. Adkins contacted Encana and inquired why this remedial work was necessary. He was told that Encana was not satisfied with the production casing cement jobs in these two wells. After inquiring about whether bradenhead pressure had been measured in these wells, he was told that high gas pressures had been measured in the bradenhead annular spaces of both wells. The bradenhead pressure in the Brown 11-2C Well was approximately 300 psi, when vented it blew down to atmospheric pressure, but quickly built back up to 300 psi once the bradenhead valve was shut. The bradenhead pressure in the Schwartz 2-15B Well was approximately 500 psi, but it would not blow down. At this point Mr. Adkins told Encana to proceed with the remedial cementing of the Brown 11-2C, but prior to initiating the remedial cement job in the Schwartz 2-15B, he required they run noise and temperature logs to define more closely the zone from which gas was entering the borehole. Remedial cementing of the Schwartz 2-15B was completed on April 5, 2004 and remedial cementing of the Brown 11-2C was completed on April 7, 2004.
On April 1, 2004, Mr. Adkins was notified by concerned citizens that gas was bubbling up in West Divide Creek and in a couple of ponds located in the northwest quarter of Section 12 of Township 7 South, Range 92 West. Mr. Adkins responded immediately by notifying Encana, traveling to the site, meeting with concerned citizens, and inspecting the area. As he had been informed, gas was bubbling vigorously up through the water in the creek and to a lesser degree in the ponds. An Emergency Response Team from the local Fire Department was also on site in response to a notification from the US EPA. After discussion with Mr. Adkins, they agreed that investigation of the cause of this gas seep should be handled by COGCC personnel. In addition, Mr. Adkins discussed the situation with Colorado Division of Wildlife staff who also inspected the site.
Mr. Adkins apprised the COGCC environmental staff of the situation and on April 2, 2004 Bob Chesson, COGCC Environmental Protection Specialist, with adjacent property owners and with Encana and Garfield County personnel, inspected the site and collected gas and water samples from West Divide Creek. In addition, he collected a sample of the production gas from the Twin Creek 1-15B Well and samples of the bradenhead gas from the Schwartz 2-15B Well and the Brown 11-2C Well. The West Divide Creek water sample was submitted to Evergreen Analytical Laboratory for analysis of benzene, toluene, ethylbenzene, and xylenes (“BTEX”), pH, and total dissolved solids (“TDS”). The four gas samples were submitted to Isotech Laboratories, Inc. (“Isotech”) for compositional and stable isotopic analysis.
On April 5, 2004, Mr. Adkins collected a bradenhead gas sample from the Morgan 12-14B(N12) Well, which is also located within one mile of the gas seep. This sample was also submitted to Isotech for compositional and stable isotopic analysis.
On April 6, 2004, COGCC staff received the results for the water sample. Benzene, toluene, and m,p xylenes had been detected at concentrations of 99, 100, and 17 micrograms per liter (mg/l), respectively. This indicated that the gas seeping into West Divide Creek probably was not biogenic methane gas (gas made by the decomposition of organic matter by methanotrophic bacteria), but rather thermogenic gas. At this point Debbie Baldwin, COGCC Environmental Supervisor, notified the Colorado Department of Public Health and Environment - Water Quality Control Division (“WQCD”) as required by our interagency Memorandum of Agreement and prepared to return to the site. On April 8, 2004, COGCC staff received the results of the gas analyses for the samples collected from West Divide Creek, the Schwartz 2-15B bradenhead, the Brown 11-2C bradenhead, and the Twin Creek1-15B production gas. Comparison of the analytical results showed that all four gas samples had similar stable isotope ratios and composition. This indicated that the gas in the bradenheads and the gas seeping into West Divide Creek are thermogenic gas from the Williams Fork Formation.
On April 8, 2004, Ms. Baldwin met with Encana personnel and their environmental contractor (Cordilleran Compliance Services, Inc.), along with Garfield County personnel and adjacent property owners. Using a March II GPS she surveyed and mapped approximately 0.5 miles of West Divide Creek from a place approximately 300 feet upstream to an in-channel beaver pond approximately 2,000 feet downstream of the main seeping area. In addition, two stock ponds (lower and upper Langegger ponds), in which gas bubbles had been observed, were mapped. Ms. Baldwin collected four surface water samples to characterize water quality upstream and downstream of the main gas seep area and in the two stock ponds. These samples were submitted to Evergreen for analysis of BTEX, methane, TDS, major anions and cations, and a number of other parameters. BTEX was not detected in any of these four surface water samples. Methane was detected in all four samples, with the highest concentrations of 0.76 milligrams per liter (mg/l) and 0.1 mg/l detected in the lower and upper Langegger stock ponds, respectively. In addition, Ms. Baldwin collected gas samples from the lower and upper Langegger ponds for stable isotope and compositional analyses. It is anticipated that the analytical results from these two samples and the bradenhead gas sample from the Morgan 12-14B(N12) will be available by April 16, 2004.
On April 9, 2004, Ms. Baldwin collected samples from four water wells, three for landowners who, at that time, did not want Encana’s consultant to sample their wells, and one for a landowner whose well was located approximately 2 miles from the seep area. These samples were submitted to Evergreen for analysis of BTEX, methane, TDS, major anions and cations, and a number of other parameters. BTEX was not detected in any of these four water well samples and methane was detected in all four water well samples. Although the methane concentrations are relatively low, an attempt will be made to collect gas samples from two of the water wells for stable isotope and compositional analysis in the near future.
Concurrently, Encana and the COGCC are conducting other activities to protect public health, safety, and welfare and the environment and to understand more completely what subsurface conditions led to this event and how to ensure that something like this does not occur again. Encana has developed and is implementing a Plan of Action to mitigate the impacts of the gas seeping into West Divide Creek, to monitor water wells and natural springs within an approximately 1 mile radius of the gas seep, to supply landowners with drinking water, to prepare a soil gas map that delineates the extent of the seep beyond the boundaries of West Divide Creek, and to survey and sample East Divide Creek. Mr. Adkins is reviewing Encana’s records related to the drilling and completion of the four gas wells within a one mile radius of the gas seep.
On April 12, 2004, Brian Macke, COGCC Deputy Director, Mr. Adkins, and Ms. Baldwin briefed the Garfield County Commissioners about the ongoing investigation of this incident and the results to date of the environmental sampling. Later that day they met with Mr. Pepi Langegger, who owns the property on which the seep has occurred, to discuss his concerns and to update him on the COGCC’s investigation. On April 13, 2004, at two separate meetings, Messrs. Macke, Adkins and Chesson, and Encana personnel met with the affected landowners and the Grand Valley Citizens Alliance to update all interested parties on the mitigation measures and ongoing environmental monitoring. In addition, COGCC staff is keeping the WQCD apprised of ongoing developments.