Abstract
In West China, MH field is typically featured with complex high challenging unconventional reservoir. Very tight conglomerate lithology composed of volcanic rock, claystone and limestone cement as the matrix with average porosity of 9.6% and average permeability of 0.96md. The buried depth of target reservoir is around 3180m. The oil production of vertical well is about 5~6t/day after stimulation (fracturing) while horizontal well production is more desirable and about 3-4 times of vertical wells.
However, the operator faced much high challenges in horizontal drilling such as unstable long open hole interval, extremely slow rate of penetration (about ~3m/hour) in abrasive, grinding conglomerate and shale cap rock (less than 1m/hour). Reservoir structural and stratigraphic uncertainty such as local formation dip changes, 3-5m thick tight sand stacked or pinch out, inconsistent shale inter-beds and oil pay lateral variations often result in unexpected exits from target pay. In current industrial downturn, XOC (Xin Jiang Oil Company) is never so urgent in pursuit of a cost-effective way to secure high efficiency horizontal drilling campaign and successful development of this kind of unconventional tight reservoir.
A pilot project of 6 horizontal wells drilling campaign was launched. The result shows that conventional drilling and measuring while drilling technology like Motor plus GR only was not adequate to address the drilling issues, improve drilling efficiency and achieve the horizontal Net-to-Gross (reservoir exposure rate) objective. However, since the latest high DLS (Dogleg Severity) RSS (rotatory steerable system) drilling technology and unique boundary mapping technology was introduced to XOC and applied in 2016, the drill efficiency and well placement NTG was significantly improved. Boundary mapping technology realized proactive real time geo-steer the wellbore to stay in target sweet spot by detecting reservoir top/bottom at 2-4m TVD away. It significantly increases space for timely decision-making and avoid unplanned exiting from target zone. The newly developed hybrid RSS drilling technology can provide as high DLS as 17degree/100feet and ensure smooth hole in a fully rotate fast-drilling way. The first batch drilling of 10 wells was completed with above technology application, horizontal section ROP increase 47.8%~103% and average footage per run increase 49.1%~59.1%.
With the success of the first 10 wells, XOC decided to extend the employment to whole MH field which will have more than 55 horizontal wells. This paper will delineate the technology application optimization through some distinctive case studies.
