How can you predict borehole instability during drilling?

1. The best way is to have wellbore stability study analysis and finding safe mud window. 2. Check the inclination and Azimuth of plan and compare to Azimuth of maximum horizontal stress 3. Check the lithology of formation which they can be instable such as shale, salt beds in the drilling section. 4. Checking nearby wells instability problems such as caving, abnormal torque & drag + mud losses and stuck pipes.

Geology is the key. Abnormal stresses relate to regional history and structural features like thrusts or fault zones. Swelling formations relate to known depositional environments. Salt formations are often thick diapirs that seismic surveys were able to detect in 1920’s. Studying carefully drilling logs from previous campaigns points out to root cause of instability issues and this task is sometimes laborious in frontier regions. As a new well is drilled, real time drilling data can reconstruct the geologic framework and show deviations from the prognostic plan. There is time to start mitigation steps if a careful drilling plan is build before hand.

The question mentioned here is how we would predict during drilling is ongoing. So the very first indication while drilling is {1.} Stand pipe pressure (SPP) difference..and ofcourse the {2.} Rate of penetration (ROP) change, {3.} Torque, WOB.. {4} Gain or losses from Mud tanks. Once we observe the change here in drilling trends it is suggested to stop and circulate bottoms up to analyze the lithology change and now comes Part 2 where we see the difference in mud gas out , mud Temperature out, mud density out and call it under balance or overbalance.

Borehole instability are a result of a lot of issues but could be grouped in 2 categories: 1- geological 2- mechanicallly induced Geomechanics studies especially when drilling in a region where there are little knowledge of formation and geopressure is essential to determine the MW require to drill without having a well control issue and without generating formation break out that will lead to uncontrollable losses Mechanically induces losses are result of poor drilling or reaming practices and are more easy to solved with the right expertise of drilling

Mud Weight Optimization: Proper mud weight is critical for balancing formation pressures and preventing collapse or fracturing of the wellbore walls. Mud Chemistry: The chemical properties of drilling mud, including pH, salinity, and additives, can be adjusted to improve wellbore stability by strengthening the wellbore and reducing the potential for hydrate formation or shale swelling. Techniques such as the addition of loss circulation materials (LCMs) to the mud system can help plug fractures and strengthen the wellbore.

after getting to know the In-Situ stresses orientation and Magnitude, and also validating the pore pressure through downhole tests, you may find out the minimum downhole pressure to avoid wellbore instability which between those geomechanics guys is called as the breakout pressure. In most of the cases breakout is close to the formation pore pressure.

On site indicators of borehole instability erratic change in ROP, pump pressure & abnormal cuttings on shaker. These factors are positive indicator for borehole instability.

To maintain wellbore stability, it is essential to use a drilling fluid of appropriate density (mud weight) to control induced wellbore stress. One method to control wellbore stability is to apply a wellbore shield which forms an ultra-low permeability barrier on the face of the formation. This thin, flexible shield minimises fluid and pressure invasion, quickly sealing pore throats microfractures to stabilise and strengthen the well.

Predicting borehole instability integrates rock strength, failure criteria, in-situ stress, and pore pressure considerations. In-situ stresses result from overburden weight, tectonic forces, and thermal effects, while pore pressure reflects fluid pressure within rock pores. These factors shape the stress regime around the wellbore, influencing rock failure potential. Geomechanical modeling, seismic data analysis, and well testing aid in estimating in-situ stresses and pore pressure. Instability may manifest as wellbore collapse, fluid influx, or formation damage. Real-time monitoring coupled with predictive analytics enables proactive instability detection and mitigation, safeguarding drilling operations and minimizing downtime.

One key aspect in planning wellbore is first,to anticipate potential interaction between the drilling fluid chemistry and the drilled formation and second, to compensate eventual issue due to lithology by treating the mud accordingly. Excessive salinity in drilling fluid can lead to rock failure by dehydrating the mud shale formation. In the other hand. appropriate mud treatment may prevent or partially mitigate with phenomenon such as clay balling.

Drilling fluid serves to remove cuttings, cool the bit, and control formation pressure. Wellbore geometry defines the shape and size of the drilled hole. These factors influence stability by creating pressure differentials, altering rock properties, and inducing thermal stresses. Understanding drilling fluid behavior and wellbore geometry is crucial. Technologies like drilling data analysis, fluid analysis, and wellbore surveys aid in assessing their properties and behavior. Instability manifestations include mud losses, differential sticking, and formation damage. Real-time monitoring coupled with predictive analytics enables proactive instability detection and mitigation, ensuring safe and efficient drilling operations.

Types of wellbore instability: Mechanical, Chemical or a combination of both. when dealing with mechanical only take care of Mud Weight and Trajectory design, however in chemical instability you should do care of mud chemicals and inhibit the drilling fluid as much as you can. In reality, we always face both of instabilities, so should take care of all the mentioned parameters!

After scanning through offset drilling reports, my next look has always been for caliber logs, especially oriented caliber logs (e.g. diameter) in vertical hole sections. If there is a noticeable directional stress field, the previous well might have drilled through it without too much problems, but only the oriented caliber log can tell you if your new well is likely to encounter more severe hole instability and if you have selected the best trajectory.

Offset well data can offer an accurate wellbore stability picture. It is necessary to have sufficient LWD or OH tools deployed and to gather high resolution images and cuttings and to have mud logging records. The driller needs to identify reservoir pressures while managing kicks and get a thorough understanding of pore pressures. If failure happens, having this information at hand can still help when the original hole is abandoned and a different path is attempted by a sidetrack. This is not an ideal situation, but it is often unavoidable if offset data does not exist. Directional drillers can also help as they try to steer, they can detect changes in stress environment. Corroborated with well site geology that becomes useful input.

I had an incident in Holland land drilling in upper hole reactive clays where the combination of a inhibitive water base polymer fluid and the PDC bit selection were incompatible and drill rate dropped to less than a meter per hour and the cutting returned to surface disintegrated stripping almost all measurable polymer from the fluid. Dilution factor went to 25% of mud system per day. DISASTER and in my opinion 90% due to bit selection.

A change in P-rate might be a tip off. I once drilled out the shoe with a biopolymer mud that wasn't inhibitive enough. P-rate went from 25-30 meters an hour down to 1-2 meters an hour. We had to make a MWD trip and tagged high going back in. Drilled to TD and saw overpull on the trip out. We stopped and circulated at tight spots and continued out of the hole. Next trip was with screens and we landed two joints high. Rock docs went crazy on the ops team, but they were the ones who had told us this was a clean sand. Amazingly even losing 10% of the reservoir this turned out to be a great well. Better to be lucky than good,I guess.

Um dos pontos importantes da estabilidade de po?os é na hora da perfura??o, devendo estar atento aos parametros durante a perfura??o para identificar possíveis desmoronamento ou fechamento de po?os, um simples incremento de press?o durante a perfura??o ou aumento do arraste podem indicar desmoronamento e dificultar a continuidade do po?o como a retirada da coluna de perfura??o, descida do revestimento. Portanto, é importante estar com fluido estabilizada, ter a análise geológica do local e estar atento aos parametros durante o processo de perfura??o para que possa agir preventivamente e corretivamente afim que n?o exista impactos na constru??o do po?o e atrasos na entrega da tarefa.

As a lesson learned, Always always try to drill as fast as you can to avoid instabilities and prevent them instead of treating them!

Torque, pressure & watch returns at the shaker. Don't outdrill your pumps & take time to circulate the hole clean. In the rush to go fast I've seen more problems resulting from cuttings packing off & pressuring up the formations.

The prevention is: 1) good drilling practices 2) mud properties all the time in good conditions, 3) check the returns all the time (specially the cutting sizes and type. 4) minimize the conection time. 5) good sold control. 6) the geologist play a esencial point in this situation.

Monitor the well, MW in / out, periodically check the shakers, evaluate the cuttings, if is a drill brake… check with offset wells ( if is any data), if is a high DLS with no previous trend, and lastly, stay with the driller as much as possible…. Feeling the well, always the well talks….