Since the foundation of the oil industry, many wells were drilled with an old design. Such wells had been limiting the reserve recovery potential. In extreme cases, some of these wells had been suspended and remedial work is now required to unlock the wells’ potential. This paper presents a case study for restoring production and increasing the salvage value of suspended wells in areas with proven production potential yet declining production yields.
Challenges for drilling the well were found in three key areas:
Sidetrack Points: The main concern in this well was the failed cement job in the 9-5/8 in. casing and the pressurized formation above the targeted reservoir that had the potential to create new fluid paths through cement channels. The pressurized formation required a very heavy mud weight of 152 pcf and managed pressure drilling (MPD) to drill the previous well and incurred losses at the same time. By increasing the depth of the sidetrack point and drilling a short radius 5-7/8 in. wellbore in less than 200 ft., the risk of the pressurized formation communicating to the new lateral was eliminated. This saved the cost of drilling two hole sizes and the cost of milling approximately 1,500 ft. of existing 7 in. liner and running a new one as illustrated in Fig-1.
Geomechanical Challenge and Petrophysical Demands: Due to fracturing needs, drilling toward a minimum stress direction was required even though this was not preferable from a drilling standpoint. The stuck pipe tendency becomes greater when compared with drilling toward the maximum stress direction in deep wells. Placing the well in high porosity zones required real-time geosteering using high-end logging while drilling (LWD) services in high dogleg environments. By using LWD technology with high bend rates, the required reservoir contact was achieved by drilling less footage than planned. Modified best practices played a major role in achieving these objectives.
Running the Liner through the High DLS (Dogleg Severity) Environment: Drilling the short radius resulted in an averaged DLS of 30 deg/100 ft where it also reached a maximum 53 deg/100 ft across some intervals. Due to a high build rate and the azimuthal change required to reach the target. The use of oil base mud and bridging materials along with constant monitoring of mud rheology allowed the liner to be deployed successfully through high DLS section. The plan for centralizers was also modified to reduce liner stiffness while still obtaining isolation from the water bearing reservoir above the target.
The success in delivering the well and returning it to production after a challenging workover job opens the door for future activity. Restoring wells by employing the short radius drilling technique provides a cost effective solution compared to conventional workover methods in many cases.