Delta Slope Method: An Application of Mudgas Stable Isotopes to Map Fracture Influenced Production in Horizontal Wells
Horizontal wells often encounter fractured intervals that may influence production rates and hydrocarbon composition. Wells drilled and affected by fractured intervals can lead to miscalculations of the in situ reservoir hydrocarbon products away from the feature. Using mudgas stable isotopes, a method was developed to map fracture influenced production in horizontal wells. Within a study area in northeast Ohio, two parallel horizontal wells were drilled in the Point Pleasant formation at a depth of approximately 6000ft true vertical depth (TVD) and approximately 1000ft apart. The wells were drilled targeting oil and high BTU gas. While drilling, mudgas samples were collected for analysis. Initial findings showed that both wells generally had increasing concentrations of methane toward the toe of the lateral. Following hydraulic fracturing, the produced natural gas BTU factor was measured lower than expected and different between the two laterals. To understand the heterogeneity of the gas, additional analyzes were run on the mud gas including stable carbon isotopes. Indications from the mudgas samples showed a potential for a secondary gas source contributing to the produced gas. The in situ hydrocarbons away from the fractured interval were unknown. To address this issue, a method to characterize and map the magnitude of the secondary source was developed. Using this delta slope method, a plug was set in the one lateral to isolate the area influenced by the fractured interval. After setting the plug, the produced gas was resampled, and the isotopes and BTU factors were measured. The produced gas BTU factor increased, and the isotopes indicated a single source of gas. These final products are believed to be a better representation of the in situ reservoir gas not influenced from secondary sources.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019