Work stories: 1999

 Diatomite [Previous ¦ Next]

One of my more successful data management projects was at Aera Energy in Bakersfield CA. Just north of LA across the Grapevine (a cross range caused by a seaward bend of the San Andreas Fault), lie a forest of oil wells on sub-acre spacing, almost a hundred years in age. Oil seeps belie a field so rich, that one simply drills and finds heavy crude just light enough to produce by steam-flooding (the project consisted of improving data management processes with the intent of reducing steam injection costs, and we'd get a cut of the savings... one way to leap into the big league!).

Geologically this was a strange province, because the producing formation is diatomite, tightly packed and very prolific skeletons of microscopic size inside which living organisms decayed into petroleum, in an area of high heat heat flow (high temperatures on the rim of the Pacific ocean with active plates and volcanoes). The organic content and temperatures were so high, that petroleum was produced literally in-place, without rocks being buried very deeply (the only analogue is in Indonesia with similar heat and burial regime, and very rich jungle vegetations being cooked into oil). Such formations had high porosity (lots of space inside and in between the skeletons) but low permeability (little if any connection between the pores in the skeletons, tightly packed as they turned into rock). There was also no deep burial of the oil-producing formations, and there is no pressure of hydrostatic recharge (pressure of water trying to reach the surface, like in hot springs along the San Andreas Fault) - the classical configuration of oilfields saw gas pushed on top of oil, itself on top of water. Here gas if there was any simply evaporated through surface cracks, water if there was any escaped through the deep faults, and oil simply sat in the tight formations from which it could not easily escape (low permeability).

Oil was also so prolific, that there was no real need for any geology or geophysics to place producing wells. One simply drilled, completed, pumped and logged often enough to track oil production. Logging here consisted however of lowering electric tools to follow the drop of the top of the oil, not the rise of the gas/oil of oil/water contact as customary. This is because there was no formation pressure pushing the oil up (no hydrostatic recharge) - oil simply drained out of the formation, like water out of a bathtub (oil and gas more commonly come out the top like froth out of a champagne bottle). In fact no-one actually really knew what happened in the rock formation above the oil as it drained! The emptied top of the formation was called air-sand, a term found nowhere else in the annals of oil production. It was real enough though: if one pumped oil out too quickly, the formation near the surface collapsed very slightly as oil no longer propped up the rock formation, and the pump jacks got jammed in very slight depressions (in fact so shallow that they're measured with laser-ranging devices used nearby to track earth movements along the San Andreas Fault). So little was needed to be known of the subsurface to produce oil over the first 75 years, that when steam was injected in a second phase of enhanced recovery (common in oilfields exceeding 50 years of age), steam did not go where it was supposed to go... and oil recovery was only marginally improved (hence my project to improve production through better data, in exchange for a cut in the savings on steam injection).