Abstract
The NWKK field was discovered in 2004 in South-Turgai Basin, Kazakhstan. Drilling campaign during an exploration and pilot operation periods showed that the field consisted of two parts – super tight western and highly fractured eastern oil pools. The main pay zone is represented by Paleozoic limestones carbonates. Both parts have been infill drilled and put under waterflooding. However, due to different rock properties secondary recover technique was designed and has been behaving differently.
Western part rock properties are poor, so the injectors have been massively stimulated, additional injection pressure facility has been applied and the issue is still not resolved. On the contrary, the east pool has been perfectly developed by waterflooding. Five injectors and twenty-two producers are not uniformly located and form irregular pattern. However, the main feature is that all injectors which are closely located to producers were completed into aquifer. That was dictated by rock properties which are characterized by high intensity of open fractures and poor matrix permeability.
The theory behind this schematic is to avoid waterbreakthrough through the high permeability flow corridors. Moreover, the idea doesn't propose horizontal displacement as the matrix permeability is too low to reach any injectivity or water advancement through the tight zone. Finally, the main goal of downdip injection is not to horizontally displace but to maintain or even boost formation pressure vertically. In other words, the aquifer is charged and stable rise of the contact happened. As the result, since the start of injection in 2014 there is no any drastic changes in watercut trend. From the beginning of the commercial production the watercut sharply increased from 0% up to 80% within one and half year and then has been slowly increasing up to 90% within 12 years without dramatic fluctuation despite the injection of water. In addition, decreasing fluid rates trend first stabilized and after flooding increased to more than 1.5 times as the reservoir pressure nearly doubled from 64 bars to 120 bars. All this led to reduction of annual oil decline rate from 30% to 5%. Thus, profound impact is observed from the water injection below the oil water contact.
That was challenging task to develop such a formation with tight matrix blocks and high angle fracture system. Fortunately, right decision on implementing waterflooding of the aquifer below the contact was made and brings great benefit from the asset in terms of boosting oil production. Nevertheless, currently, engineers consider implementing the cyclic water injection to further improve secondary oil recovery method which already proved to be efficient for highly fractured reservoirs.
