Theoretical Aspects and Practical Implementation of Study of Drilling Fluid Level in the Annulus While Drilling with Total Losses

Day 2 Wed, May 26, 2021

Echevarria

2021

Carbonate formations around the world and specifically in a Middle East are prone to have total losses while drilling. And the nature of the losses often related to the highly fractured formations of the pay zone. When such fracture(s) is crossed by the wellbore the lost circulation initiated and led to a drilling without a return to a surface. To avoid undesired well control event or wellbore instability and to maintain the constant bottom hole pressure the mud cap drilling strategy often used as a preventative measure. The mud cap can be either the continuous or based on some volume or time interval, depends on the local practices or the policy of an operator. The mud cap flow rate as well as mud cap mud weight are often based on the best practices, not supported by an engineering study. To understand the behavior of the drilling fluid level in the annulus while drilling with total losses the drilling bottom hole assembly equipped with annular pressure while drilling tool was used. As the drilling required to use the continuous mud cap, then the specific guideline was developed on measurement of the bottom hole pressure and further conversion of it to the fluid level. The study was performed across pay zone with one or several loss circulation zones identified. As the result it was confirmed that the used mud cap flow rate had minor to none effect on the fluid level position in the annulus and that the bottom hole pressure remained the same. It showed as well that different loss zones are behaving in a different way, what can be considered as a factor affecting their ability to be sealed. The obtained knowledge and the information should help to understand better the loss circulation behavior as well be an important step toward development of the product which may cure the losses in high fractured carbonate formations. The results of the study can be implemented in any other project or a field.

The Theory and the Practical Validation of the Fluid Level Position in the Annulus During Lost Circulation

Day 2 Wed, May 26, 2021

Echevarria

2021

Deployment of Downhole Mechanics Measurement System and Drilling Dynamics Modelling to Enhance Overall Drilling Performance Under Complete Mud Losses Environment

Garnica

Moreira

SPE/IATMI Asia Pacific Oil &Amp; Gas Conference and Exhibition

2021

Drilling surface 16-in. and 12.25-in. sections in Middle East often accomplished by complete mud losses where downhole dynamic changed completely. To increase the performance and reduce drilling time the Positive Displace Motors (PDM) are used, however drilling under complete mud losses scenario may lead to a failure of the PDM, Measure While Drilling (MWD) tool, jar and any other components of the Bottom Hole Assembly (BHA). This manuscript describes the study of BHA dynamic in total loss scenario aiming to increase Rate of penetration (ROP) and decrease mechanical failures. The changing in drilling dynamics under complete mud losses increases the severity of shock and vibrations (S&V), BHA whirl and, consequently, leads to downhole failures. Local practices have been used to control this risk by taking an over conservative approach, limiting Weight on Bit (WOB) and Revolution per Minute (RPM) to very low levels, affecting overall performance. To comprehensively understand the level of shock and vibrations under complete mud losses based on the modeled data, a Downhole Mechanics Measurement (DMM) system was used in the BHA to acquire the required data in real time to confirm and further improve the modeling of drilling dynamics. A drilling schedule with several combinations of WOB and RPM was developed to cover the full drilling envelop. This study provided valuable understanding on the drilling dynamics while drilling under complete mud losses and allowed to clearly define the limiting boundaries to optimize ROP without jeopardizing the mechanical integrity of the BHA, particularly the PDM and drilling jar. On each formation drilled, RPM, WOB were changed to cover all possible combinations and, using the continuous real time measurement, ROP was optimized based on the level of shocks and vibrations experienced. Furthermore, the recorded mode Low and High-frequency data enabled to model the drilling dynamics and to quantify the effects of shocks and vibrations on the BHA. As a result, the wells have been drilled with significant ROP improvement (saving one day per run) and without downhole failures, achieving higher than expected performance results.

Quantification of the Loss Conduit Aperture During Lost Circulation in Fractured Carbonates

Day 1 Tue, October 12, 2021

Johnson

2021

Fractured carbonate formations around the world are prone to lost circulation that not only affects the well construction process but creating a longtime effect on the wellbore integrity. Despite multiple attempts to cure them the success rate is usually low. This manuscript is aiming to provide a new vision on the reason of lost circulation across carbonates. To have better understanding of the complete losses across the fractured carbonates the series of studies were initiated. At first to understand the strength of the loss zone the fracture closing pressure was evaluated via study of the fluid level in the annulus and back-calculation of the drilling fluid density effect on it. Secondary, the rock properties across the loss circulation zones were studied by using the microresistivity images, dip data, and imaging of fluid-saturated porous media. At last, the trial tests with different treatment materials were performed to evaluate the effect of it on curing the losses. The results of the studies brought new information and explained some previous unknowns. The formation strength across lost circulation zone was measured and it was confirmed to remain constant despite other changes of the well conduction parameters. It was also confirmed that the carbonates are naturally highly fractured having over 900 fractures along the wellbore. The lost circulation zone was characterized, and it was confirmed that the losses were not related to the fractures but rather to the karst, dissolution and to mega-fractures. The size and dip of the fractures were identified, and it was proven the possibility to treat them with conventional materials. However, the size of identified mega-fractures and karst zones exceed the fractures by 100 times in true vertical depth, and in horizontal wells the difference is thousands times due to measured depth. This new information explains the previous unsuccessful attempts with the conventional lost circulation materials. Further based on the newly available information the mathematic description of the lost circulation zones was provided.