KSA is now reaching the point where the easy production of oil, as in sink vertical wells at kilometer intervals and watch an average of 10 kbd merrily bubble to the surface, is now largely over. Increasingly the oilfields are moving into the more advanced, and costly, procedures that help sustain a production that would, under earlier production regimes, by now have long faded into memory. Ghawar, for example, is moving into CO2 injection and some steam assist (likely with the areas with heavier, tar-ier deposits) seeking to maintain an overall 5 mbd production. But today I want to talk a little about their increasing use of hydraulic fracturing of their horizontal wells, and a little more technical detail about growing cracks through rocks. Consider the problem that high production fields have, when a horizontal well runs through a high permeability, or densely fractured zone. The impact of this on premature water breakthrough is well documented. The relative preferential movement, for example of water along faults can be seen in this model from Ghawar.
It is also evidenced by this simulated model of the effect of high fracture densities on the performance of MRC wells, where increasing the drawdown pressure to pull fluid into the wells can lead to premature watering out of the well.
Figure 2. Use of a low draw down pressure to maintain oil flow.
With low draw down, the flow rates are reduced, but the fluid entering the well remains largely oil (Mubarak et al) In contrast if the differential pressure is increased (by lowering well pressure) then the greater flow rates allows the underlying water to flow up the fractures and prematurely waterflood the well.
Mubarak et al)
It has been obvious to Aramco (who run the KSA fields) for some time that adding their own fracture paths to the field would result in better performance, and could also help overcome the problem of natural fractures and high-permeability zones such as those known as the Super-K in Ghawar.
Rahim and Al-Qatani )