Understanding magnetic enhancement in hydrocarbon reservoirs

A detailed magnetic study has been undertaken for over 115 samples of 12 wells in the Brazeau area of the Devonian Nisku formation, Alberta Canada. I report a range of magnetic results including room temperature hysteresis, first-order reverse curve (FORCs), low-temperature magnetometry, high-temperature magnetic susceptibility results, Scanning Electron Microscopy (SEM) results of samples from sour gas pools, sweet gas and oil pools, and dry well. The sour gas pools had the strongest magnetization, followed by the sweet oil and gas pools, while the dry well had the weakest magnetization from the room temperature results. There was observable strong magnetic enhancement at the hydrocarbon fluid contact for some wells particularly the sour gas wells, while some did not have anomalies exactly at the contacts but few meters away from the contact. These anomalies are suspected to be paleo-contacts. This observable magnetic enhancement was caused by inorganic precipitation of interacting single domain hematite (0.03-0.08 μm), multidomain magnetite with a vortex (3 μm above), and SP (˂0.03 μm) greigite and pyrrhotite nanoparticle magnetic minerals at the hydrocarbon contacts. Iron oxide and sulphide minerals were revealed to be present in all the wells both from low and high-temperature measurements and also with the FORC analysis showing high coercivity ~100-350mT. From the data, iron sulphide greigite and pyrrhotite appears to be in dominant proportion alongside other minerals. I had the strong presence of siderite, greigite, and pyrite in the sour gas pools, and monoclinic pyrrhotite and maghemite in the sweet oil and gas pool and background presence of detrital magnetite, hematite, and siderite in the dry well. Authigenic magnetite and hematite were equally present in all the hydrocarbon wells. However, iron sulphide greigite and pyrrhotite appears to be in dominant proportion alongside other mineralsOpen Acces