How do you ensure wellbore stability and integrity during drilling?

A successful well construction activity starts with a detailed PPFG and WBS study using offset well information. Identifying the root cause of hole problems in offset wells assist in drilling fluid and cement formulation as well as well trajectory. Detailed review of geology reports with special attention to sticky clays, well bore breakouts and cavings assist in being alert for potential issues. Real time monitoring of drilling data and any abrupt changes to the normal trend could be used as an early indication of potential hole problems. Sometimes looking at logs and determining hole ovality will assist in mud weight adjustments. In case, downhole losses exist, the WBS related issues could be worsened.

After the rig the drilling fluids is probably the next most important service when drilling a well. Is the information on the daily mud report correct? How do you ensure it is correct? Is the mud engineer, service rep or drilling engineer able to evaluate down hole conditions? Can they then adjust the density, rheology, bridging agents, hydraulics, etc as necessary? Stay safe.

Another key "Formation Related" step in wellbore stability analysis which has to be taken cared at the very beginning of the project is "Mechanical Stratigraphy" which is mainly classification of formations into SHALES and Non-SHALES. It will help to have a wise judgement on using the most accurate pore pressure modeling method in the sequence of interest. By having a proper mechanical stratigraphy onboard, pore pressure in shales can be modeled using the known estimation methods like Eaton and Bowers to reflect over-pressure zones. On the other hand, pore pressure in non-shale formations (i.e. carbonates and sandstones, mostly in reservoir section) can be handled using formation pressure measurements like MDT, RFT, RDT, XPT and PLT.

Young’s Modulus is critical in hard rock basins such as the Arkoma and Illinois. The drilling fluid of choice is Air, however just before kicking off on a directional well, we mud up. Air can support homogeneous horizontal wellbores but both of these basins—and in general most basins—are Far from homogeneous. At this point in your drilling program, skin, boulders, clay swelling and a host of other considerations come into play… in addition to wellbore stability per se’.

From Wellbore Stability point of view, the most important MUD parameter to be modeled for a safe and fast drilling is mud weight including ECD (Equivalent Circulating Density) and ESD (Equivalent Static Density). With a proper mud weight, drilling operation will continuously proceed in "Stable Mud Window" and hazardous boundaries (Kick, Breakout, Induced Fracture and Breakdown) will be safely un-touched. In chemically problematic shaly formations, also mud salinity and mud water content are playing dominant role to control water exchange between drilling fluid and chemically unstable shales. This way, shale dehydration (due to high mud salinity) and shale swelling (due to high mud water content) will not happen.

As Wellbore stability side, Drilling fluid need to be designed as considered formation lithology chemically; such as shale content / Salt dome formations or swelleble shales. In physically; some of shales maturity plays an important role while drilling if section drilling take up long time that shale stress can not tolerate the pressure differencies and collapse. Finally; for safe and fast drilling activities Constant bottom hole pressure which is MPD technique needed for as my perspective.

Before even facing any issue while drilling, in complex geology setups and problematic formations (most importantly shales), it's good to oversee the drilling mechanical challenges while well trajectory design phase to diminish the drilling hazards. A very helpful approach in trajectory design for problematic formations is "Trajectory Sensitivity Analysis" which provides the optimized inclination and azimuth in the target zones, and the proper mud weight for the given trajectory. Using this approach, we can have a robust understanding about the maximum allowed inclination and azimuth to pass shales and problematic formations without any major problem. Field scale faulting regime and the associated stress model plays an important role here.

Cmt & Csg design is playing very important role as a means of wellbore stability,Cmt need to be designed considered lithology chemically as means of salt content and water.Cag&Cmtoperation need to be designed considered ECD of cement before Oprtion especially after hang liner displacmnt rate plays imprtn role because of narrow space in overlap section creates tremendous pressure that exposed to formations; it can cause loss. Third perspective is that sufficient cement basket and Cement basket and centrilizers design plays an important role as my perspective. In some cases thixyotropic cement or other cement techniques needed for special jobs or before Cmt operation pump LCM or gung plugs to increase wellbore stability plays importnt role.

In addition, MPD Techniques will be very helpful to maintain wellbore pressure constant as considered formation porepressure and formation fracture gradient.

From my experience, a potent Wellbore Integrity Management System hinges on several pillars. Harnessing risk assessment tools helps fine-tune well designs and operations, reflecting diverse geologies. Embracing sensors facilitates real-time tracking of key metrics, a crucial step in early anomaly detection. Efficient data handling, leveraging AI, anticipates challenges. Quality checks, especially in cement and against corrosion, extend equipment life. Regular pressure tests, maintaining barriers, and continuous personnel training ensure consistent integrity. Always staying updated with regulatory standards, having a crisis blueprint, and learning from feedback are my golden rules.

Oil based mud, very very low fluid loss over extended time, balanced salinity, good hole cleaning, proper tripping techniques, i.e. low flow low roll when struggling to avoid packoffs, smallest possible PSD in bridging package, nano if economical, its the whole package that will assure getting that casing to TD.

Considering a very important factor in overall field scale and well scale stability (TIME) is also critical. Preparation of Geomechanical Wellbore Stability programs should be continued while the field is under exploration, in production phase, or late period of life cycle while using EOR/IOR methods. While production (depleting the reservoir pressure) or while injection (building the reservoir pressure) time plays a dominant role which has to be addressed through 4D Geomechanical modeling. While both depletion or injection, having an altered pore pressure factor, effective horizontal and vertical stresses will also change. 4D modeling method provides a good forecast of drilling/ production optimization in field's life cycle.

Assuming we can manage the other factors…. It’s usually about hole cleaning and pack off that destabilizes formations. Avoid pack off (include staying out of the ‘avalanche zone’ as much as possible) and you have a good chance to deliver a successful hole section.