Rapid Methods for Locating Existing Well Penetrations in Unconventional Well Development Areas of Pennsylvania

Hammack, Richard (National Energy Technology Laboratory) | Veloski, Garret (National Energy Technology Laboratory) | Sams, James (National Energy Technology Laboratory)



Pennsylvania has a 150-year history of oil and gas production-the longest of any state- and this enduring activity has resulted in the drilling of more than 330,000 known wells. However, unknown wells may exist because innumerable wells were drilled during Pennsylvania's early years of intense oil and gas development when incomplete records were kept of well locations. The concern is that early wells are likely to be unsealed because there were no laws that required effective plugging when the wells were abandoned. Now, many unrecorded wells are thought to be in areas of emerging shale gas and shale oil development where open wellbores might provide a pathway for undesired upward migration of fluids and gas from hydraulically fractured reservoirs. Because of this concern, Pennsylvania regulators have asked operators to locate orphaned and abandoned wells within a 1000-ft- buffer of new wells before hydraulic fracturing.

The National Energy Technology Laboratory conducted high-resolution, helicopter magnetic surveys over four large land tracts in western and north-central Pennsylvania where historic oil and gas production has taken place and where unconventional oil and gas resource development is occurring or expected. The project's objective was to evaluate the ability of helicopter magnetic surveys to locate existing wells in heavily vegetated areas of varying terrain. Magnetic surveys locate wells by detecting the unique magnetic signature of vertical, steel well casing, which is depicted on magnetic maps as a "bull's eye" type anomaly centered directly over the well. To mitigate for the likelihood that wellbores exist where most or all casing has been removed, this study augmented helicopter magnetic data with supplemental information from farmline maps, state well databases, historic air photos, and digital terrain models generated from LiDAR datasets- all information that is publically available for areas within Pennsylvania.

The four surveyed areas include: 1) a 7 km2 (2.7 square mile) tract of privately owned land in Washington County with historic oil and gas production and where gas is now being produced from five, horizontal Marcellus Shale wells; 2) a 17.7 km2 (6.8 square mile) area of state owned land (Hillman State Park) in Washington County with historic oil and gas production and where the uppermost well casings were often cut off or buried by 1950's era surface coal mining; 3) a 28 km2 (10.8 square mile) block of state-owned land in the Susquehannock State Forest of Potter County where gas was once produced from the Oriskany Sandstone, but it is now a gas storage field; and 4) a 37.7 km2 (14.6 square mile) area of state owned land (Oil Creek State Park) in Venango County, which contains more than 900 known wells, including some of the oldest oil wells in the United States. Ground surveys to confirm well targets from the helicopter magnetic surveys have been completed for two of the four areas flown including: 1) the private land tract in Washington County, PA with Marcellus Shale development and 2) the area in Susquehannock State Forest that is now a gas storage field.

At the private land tract in Washington County, the helicopter magnetic survey identified 13 well-type magnetic anomalies within 1000 ft of the five horizontal Marcellus wells located there. The ground investigation confirmed that nine well-type magnetic anomalies were wells while four magnetic anomalies were found to arise from non well sources. One additional well with a weak (initially overlooked) magnetic anomaly was found using historical air photos. Of nine confirmed wells, six wells had recorded locations in Pennsylvania's statewide oil and gas wells database (PA*IRIS/WIS). However, the PA*IRIS/WIS locations were sometimes too inaccurate for the wells to be located in the dense underbrush.

At the gas storage field in Susquehannock State Forest, the helicopter magnetic survey identified 81 magnetic anomalies, including 55 well-type magnetic anomalies. A subsequent ground investigation confirmed that 30 of the 55 well-type magnetic anomalies were well locations. All confirmed wells except one were listed in the PA*IRIS/WIS state oil and gas well database and the locations provided were sufficiently accurate to locate the well in the field. The helicopter magnetic survey also identified two gas transmission pipelines with pulsed cathodic protection and multiple short pipeline segments without cathodic protection.

Helicopter magnetic surveys identified 192 well-type magnetic anomalies within Hillman State Park and 742 well- type magnetic anomalies within Oil Creek State Park. The ground investigation to confirm well locations in the two state parks had not commenced at the time of this report.

Preliminary observations from this study are:

the PA*IRIS/WIS well database is incomplete for wells drilled between 1890 and 1920, the era of early well drilling at the Washington County Marcellus Area. Only six of nine confirmed wells were listed in this database.

the PA*IRIS/WIS well database contained 29 of 30 wells found by the helicopter magnetic survey at the gas storage field in Susquehannock State Forest. Wells in this area were drilled post-1950 to produce from and store natural gas in the Oriskany Sandstone. This area contains active gas storage wells and plugged and abandoned gas wells.

high resolution magnetic surveys acquired from low-flying aircraft provide accurate locations for wells with steel casing. However, wells with no steel casing exhibit weak or no magnetic anomaly.

the inspection of publically available historic air photos or LiDAR imagery for well signatures can sometimes augment helicopter magnetic surveys by identifying well locations where the steel casing was recovered for reuse or salvage.

complete casing strings are not needed for detection by helicopter magnetic survey although the minimum casing requirement for detection is not known.

  Country: North America > United States (1.00)
  Geologic Time: Phanerozoic > Paleozoic (0.46)
  Industry: Energy > Oil & Gas > Upstream (1.00)