oil sweep and volumes

in response to a request by 247

The following applies to all oil reservoirs - skip to the last 2 paragraphs if you trust me or are jargon adverse

Oil is contained in pores in the rock (written as a percentage), permeability is a measure of how connected these pores are (the better the connection the faster the oil will flow and the better the sweep).

The sweep radius is the distance oil will travel to get to the well bore and then to the surface. Porosity/Permiability affect the sweep radius but so do many other complicated factors (oil viscosity, temperature, reservoir configuration, faulting and on and on). The actual sweep radius can be estimated crudely but realistically it is a 'let the reservoir produce and see what happens'.

World practise for reservoirs like Snatcher (200-500 bopd clastics with light faulting) is to drill on 160 acre spacing and infill to 80 acres (and if the sweep radius is low or oil production makes money by accelleration).
Snatcher 1 2 and 3 look to be on 160s while Charo looks like infills to 80s so I am assuming Snatcher may get some infills (unless all the oil can be drained on 160s)

Pressure - all bottles of oil held deep in the earth are under pressure. When the pressure is released in one part of the field - all the wells see the pressure drop. As the pressure drops the oil is produced slower (and this lose of kinetic energy is suplimented by pumps). This is the main way companies tell whether oil fields are connected.

Oil Water contact - most fields (certainly in the Cooper/Eromanga) have a 'spill' point where below the contact oils spills out so the upside down salad bowl only contains oil to a certain level. If 2 wells have the same oil/water contact it means they may be in communication but this is not certain (complicated reasoning for another time).

The volume of oil contained in the pores and more importantly the amount you can produce is a highly complex and uncertain number that is continually estimated until the wells are abandoned.

Sorry for the long intro - so in the case of Snatcher-Charo the releases have stated that Snatcher 1 and Snatcher 2 have the same contact and are more importantly in pressure communication to Charo 3 (and supposedly to Charo 6 which is between C3 and S1). So all 4 wells are part of the same field. This means they will all be at the same pressure and given equal porosity/perm and pumps they will all do the same rate and start radially sweeping oil from near the well bore and then gradually draining the reservoir. For the 'border region' only Snatcher 1 and Charo 6 matter. They are ~400 meters apart and on slightly less than a 80 acre spacing. Each well will undoubtably be pumped at maximum and sweep all the oil it can in partial competition. The rest of the field will largely be unaffected by the wells across the border and in the case of Snatcher, I would assume they will keep chasing the field to the NW and refine the estimated volumes as they go along and infill the current wells if neccessary.

Summary of the summary - a political border seldom affects how much oil each side gets but there is synergy with the operators working together on the topside. The volume and value of Snatcher is only enhanced by the field extending to Charo since this suggests a more areally extensive oil field.