Planning of an MPD and Controlled Mud Cap Drilling CMCD Operation in the Barents Sea Using the CML Technology

Abstract

The subsurface formations and reservoir conditions encountered in certain areas of the Barents Sea offer some unique challenges for the operators and the drilling industry. These areas of the Norwegian Barents Sea consist of naturally fractured and weathered carbonate formations which may incorporate open karsts. Drilling into large open fractures or karsts will result in total losses and mud cap drilling practices must be employed to enable further progress. Such locations may require some unique solutions to drill effectively and safely while conforming to local rules and regulations; including deploying winterized rigs capable of year-round operations in Arctic environment. This paper describes the process of selecting a viable solution for drilling in such an area where potential mud cap drilling practices could be required, the rig integration process, class notation process, development of operational procedures, risk assessment, training and testing of equipment prior to commencing the operation. This was a fast track project which incorporated developing new mud cap drilling procedures and processes when operating the Controlled Mud Level (CML) system. Since mud cap drilling practices from a floater on the Norwegian Continental Shelf (NCS) is a rare occurrence, it required close cooperation between the operator, the drilling contractor and the service provider. To facilitate the process and assure sound practices a third party with experience on mud cap operations was also engaged. The paper will also briefly describe the Controlled Mud Cap Drilling (CMCD) principle and the results from drilling the well.

Real-Time Detection of Karstification Hazards While Drilling in Carbonates

“…For example, Shell reported that total losses were observed in each of the six wells when drilling in carbonates in Sarawak (Peninsular Malaysia) [30]. Similar problems exist on the Norwegian Continental Shelf when drilling into open fractures or karsts resulted in total losses during a week [20,31,32]. Two to four weeks of non-productive time were reported by an operator company in Qatar when a large volume of cement was pumped to plug intervals of mud losses in carbonates [33].…”

“…The range of applications of this methodology is linked to the accuracy of delta-flow measurements. Delta-flow analysis presented in this section is based on precise measurements of the inflow and outflow using flowmeters integrated in a Controlled Mud Level (CML) system [31], which was utilized in drilling in the region of our study.…”

Use of a Transient Model for Studying Kick Migration Velocities and Build-Up Pressures in a Closed Well

“…The discrepancy was that in small scale experiments and full-scale test wells, the gas velocity was estimated to be around 100 ft/min while field estimates indicate gas rise velocities of only 15 ft/min. This discrepancy is still around as seen in [2,3] Recent fields observations from pressurized mud cap drilling operations seem to indicate a very low gas migration velocity [3]. However, it is not clear from literature how the gas velocities were estimated for these field observations.…”

Prediction and Early Detection of Karsts—An Overview of Methods and Technologies for Safer Drilling in Carbonates

“…For a better understanding of karst objects and their effects on drilling, we refer interested readers to the studies in [24][25][26] on drilling in karstified carbonates in the Loppa High region in the Barents Sea which classify karstification objects into dangerous and not dangerous for drilling.…”

“…A comprehensive analysis of borehole images and the history of drilling revealed that karsts larger than 0.5 m pose significant risks for drilling since they lead to a partial or total loss of the drilling fluid, thus compromising drilling safety [24,25]. In some cases, BHA components were broken due to excessive shock-loading when the drill bit drops to the bottom of the cave.…”