reservoir . . True underbalanced drilling of the taranaki limestone is the only method to guarantee maximum reservoir protection for any type of oil or gas reservoir.
Perhaps they stopped because if the were too high, they would intersect the solution gas which may be the primary production drive mechanism. If this pressure was relieved prematurely it would kill the drive mechanism that delivers the oil to wellbore. If oil has gas in solution at high pressure 4000-5000psi then it may come out at low pressure. The seismic at the structure they targeted is ripe for mis-interpetation so they may have wanted well logging prior to making the next multi-million dollar decision. The OOIP is affected by how the completion of the fractured limestone is addressed. The volume that can ecer be produced is dependent on HOW they proceed. The only success, data, know how is in the wells and data that have already been produced at depth and in the manner they were done. Technology has improved since the original explorers pioneered their way to production. We wouldn't use their methods today verbatim. They said they had mapping of the formation. They can't have mapping from douglas as it wasn't productive if they lost circulation. They now have logs for douglas and pukatea so they can identify cutoffs for low limits of porosity, permeability and water saturation - all which help map thickness of unproductive and potential productive zones. They knew where oil/water contact was, if they have temp, rates from nearby they can make napkin sketch of what potential is there. Drainage is a big question, if they have good drainage the pressure could be very high, the flow rate would also be very high.
Now onto the reservoir itself, the irreversible damage that would have been done to the reservoir would have included; pore plugging, fracture plugging, shallow matrix damage, filter cake inside wellbore, caused from forcing fluids, drilling mud filtrate and cuttings into the target formation.
To avoid this they need to maintain a steady bottom hole hydro-static pressure with continuos circulation. They also need to use reservoir friendly fluids. They need a way to monitor downhole conditions in realtime to confirm the downholw fractured limestone reservoir is in a constant underbalanced state. They need a bha design that will ensure no leak-off of overweighted drilling muds don't penetrate into the producing section of the wellbore. Mostly they need to avoid the ;ost circulatiom problem which they know they will have from the offset wells they referred to, and as mentioned with Douglas-1 which lost circulation and then its game over.
To pull this off they need data monitoring that will give them real-time data at surface from downhole. The tool would need a mechanical tool string release tool in the event of a sidetrack. The tool would need to have over engineered circulative valve to make sure the geoscience time get superior wellbore cleaning of cuttings.
Plus the government scientists would want software recordings at surface of what happens as it happens with wellbore pressures. If they have to clean the hole while drilling into such a fractured zone they can do wiper trips if they have a hydraulically operated motor by-pass system with reverse oriented circulation ports to make certain the drill cutting are properly transported to surface for geologists and drilling decisions on site and remotely.
To drill underbalance with rotary is sold as such, yet true underbalanced is for the long life of the reservoir. They need to eliminate the pressure spikes caused downhole that occur everytime with jointed pipe because they have to shut the surface pumps off everytime they add a section of pipe. The continuous coil pipe has no connections to add making the need to shut pumps down not necessary. The column to 3100m of drilling mud shocks the producing reservoir and plugs the fractures, pore spaced when the slug of drilling mud come sloshing down.
Depending on the payzone thickness controlling the steering is going to require efficient hole cleaning and bit control, the technology to do all of the above is complex.
To sum up, minimize formation damage, maximize cuttings transport, eliminate differential sticking by having ability to continuous circulation by maintaining a constant bottom hole circulating pressure. To keep the cost down they need an rop that is improved by the hole cleaning ability of the bha continuous circulation. Use less expensive drilling fluids that won't damage reservoir by avoiding polymers and chemicals that damage the shallow matrix, fractures and pores. Obtain better more accurate samples, maintain control of production inflows and most important avoid pressure surges from starting and stopping the pumps which are a reservoir engineers nightmare.
My 2 cents. not here to create drama, nor play games, just offering a perspective that i think has been overlooked by some, ignored by others. They will build an field here, in the right time, manner that makes sense for the long life of a field.