Gas Detection In Upper Cretaceous Formations

Abstract

Abstract Hydrocarbon resource companies in the Lloydminster heavy oil region have experienced problems with unwanted gas flows to surface outside production and surface casings. Locating the source of these flows prior to attempting to shut the gas off has proved troublesome. Gas shut-off attempts have therefore had varying degrees of success ranging from failure to expensive success. Thus paper illustrates how conventional wireline gas detection methods, although successful in detecting gas sources in the Mannville sands, failed in the Upper Cretaceous horizons. Relatively unconventional wireline techniques are shown to be reasonably successful in locating these Upper Cretaceous gas zones. Studies prior to and after utilizing these unconventional techniques are also discussed. Finally, suggestions are made for wireline logging practices and remedial techniques Introduction Unwanted gas flows to surface outside production and surface casings has become a matter of concern in recent years in the Lloydminster area. Aside from the obvious safety hazard posed by this problem, there can be severely detrimental environmental effects should the gas be allowed to migrate into the surrounding soil. Many cases of dead vegetation have been documented as a result of this gas migration. Quite often the unwanted gas flows to surface are not immediately obvious. Much of the time dead vegetation around a newly completed or abandoned well is the first indication that a problem exists in a newly explored heavy oil area. With this in mind, most hydrocarbon resource companies have begun to monitor the area around their wells with gas detection devices, especially in fields that are known to be gas prone. Conventional methods of downhole detection were attempted on individual wells. It was eventually discovered that these methods were inadequate. A modified system of gas detection resulted. The unwanted surface gas flow problem occurs in many areas around Lloydminster. The authors chose an area south and east of Lloydminster as a basis for this paper (Fig. 1). The results of the modified gas detection system in this area will be discussed in light of the historical and geological information available. History and Geology During the period from 1950 to 1965 numerous 120 mm Road Allowance Stratigraphic Tests were drilled, logged and abandoned between the townships of 44 to 54 east of the Alberta – Saskatchewan border (Fig. I). The purpose of these stratigraphic tests was to define the stratigraphy of the area and to outline the hydrocarbon potential of the zones penetrated. A typical geological pattern evolved from these wells (Fig. 2). Some of the Mannville sands were found to be oil-bearing, No obvious hydrocarbon showings occurred in the Upper Cretaceous formations above the Mannville horizon. Once the stratigraphy and hydrocarbon information was extracted, these wells were required to be abandoned by cementing any potable water zones in the glacial till and by cementing any potential hydrocarbon-bearing zones. As there appeared to be no hydrocarbon potential in the Second White Specs, Colorado Shales or the Lea Park zones, governmental agencies of the day did not require these zone to be covered by cement (Fig. 3).