TY - THES

T1 - Investigation of drilling fluid performance

AU - Werner, Benjamin

N1 - embargoed until 27-05-2016

PY - 2014

Y1 - 2014

N2 - The increasing need for extended and ultra-extended reach wells challenges the current technologies. The top drive, the drilling components, as well as the hole cleaning and borehole stability reach their limitations to exploit the ever deeper oil and gas reservoirs. One major limiting factor are the torque and drag forces acting on the drillstring. A current investigation of SINTEF Petroleum Research considers a borehole with rifle shaped helical grooves inside the borehole walls as an option to overcome the named limitations. These grooves shall reduce the contact area in horizontal and inclined wellbore sections between the drillstring and the formation. This is leading to a higher contact pressure over reduced contact area and resulting in friction reduction. To research the actual benefits of this concept, a custom made flow loop was designed. Consisting of a 12 m long inclinable test section with a wellbore made of concrete. The experimental rig can be set up with a circular or the non-circular rifle shaped wellbore profile. A steel rod representing the drillstring is located eccentrically inside the test section and allows free lateral whirling motion. A sand injection and separation unit enables the buildup of a sand bed, and tests regarding the hole cleaning properties and cuttings removal. For the latest experimental campaign the two water-based drilling fluids, potassium chloride and bentonite, were tested with the circular wellbore profile to investigate their hole cleaning performance. For comparison reasons, both fluids were designed to have a similar viscosity, following the Herschel-Bulkley model. To measure the viscosity a standardized Fann viscometer was used throughout the whole experimental procedures. The experiments on the flow loop were divided into tests regarding the pressure gradient without sand injection, and tests about the sand bed build up and hole cleaning with sand injection. Thereby the sand represents the emerging cuttings of an actual borehole. Different fluid velocities and drillstring rotations were the varying parameters. A challenging task was the preparation and upkeep of the desired viscosity profile due to the large amount of fluids and sand particle influences from the experiments with sand injection. Furthermore, the potassium chloride fluid showed an increased foam and air bubble development. A completely similar viscosity curve for both of the fluids was not reached. The difference accounted to 5%. The results for the experiments without sand injection showed a higher pressure gradient for the potassium chloride fluid. The bentonite fluid demonstrated a slight dependency on the drillstring rotation. A higher pressure gradient resulted from higher rotational speed. The experiments with sand injection point out better hole cleaning capabilities for the potassium chloride fluid at lower fluid velocities and a better hole cleaning performance for the bentonite fluid at higher fluid velocities. It can be concluded that the handling of these drilling fluids is a sensitive task. More rheological analysis is necessary to fully understand the behavior of both fluids. The experiments showed that higher drillstring rotation benefits the hole cleaning. In general both fluids act differently regarding their hole cleaning performance. To investigate what causes these differences, further work could consider to experiment with different sand rates to show the limitations of the sand removal capabilities. Furthermore the gelling properties can be investigated as well as the influence of the air bubbles. Experiments with lower, respectively higher fluid velocities could give information about the variances of the two fluids during the sand bed hold up tests.

AB - The increasing need for extended and ultra-extended reach wells challenges the current technologies. The top drive, the drilling components, as well as the hole cleaning and borehole stability reach their limitations to exploit the ever deeper oil and gas reservoirs. One major limiting factor are the torque and drag forces acting on the drillstring. A current investigation of SINTEF Petroleum Research considers a borehole with rifle shaped helical grooves inside the borehole walls as an option to overcome the named limitations. These grooves shall reduce the contact area in horizontal and inclined wellbore sections between the drillstring and the formation. This is leading to a higher contact pressure over reduced contact area and resulting in friction reduction. To research the actual benefits of this concept, a custom made flow loop was designed. Consisting of a 12 m long inclinable test section with a wellbore made of concrete. The experimental rig can be set up with a circular or the non-circular rifle shaped wellbore profile. A steel rod representing the drillstring is located eccentrically inside the test section and allows free lateral whirling motion. A sand injection and separation unit enables the buildup of a sand bed, and tests regarding the hole cleaning properties and cuttings removal. For the latest experimental campaign the two water-based drilling fluids, potassium chloride and bentonite, were tested with the circular wellbore profile to investigate their hole cleaning performance. For comparison reasons, both fluids were designed to have a similar viscosity, following the Herschel-Bulkley model. To measure the viscosity a standardized Fann viscometer was used throughout the whole experimental procedures. The experiments on the flow loop were divided into tests regarding the pressure gradient without sand injection, and tests about the sand bed build up and hole cleaning with sand injection. Thereby the sand represents the emerging cuttings of an actual borehole. Different fluid velocities and drillstring rotations were the varying parameters. A challenging task was the preparation and upkeep of the desired viscosity profile due to the large amount of fluids and sand particle influences from the experiments with sand injection. Furthermore, the potassium chloride fluid showed an increased foam and air bubble development. A completely similar viscosity curve for both of the fluids was not reached. The difference accounted to 5%. The results for the experiments without sand injection showed a higher pressure gradient for the potassium chloride fluid. The bentonite fluid demonstrated a slight dependency on the drillstring rotation. A higher pressure gradient resulted from higher rotational speed. The experiments with sand injection point out better hole cleaning capabilities for the potassium chloride fluid at lower fluid velocities and a better hole cleaning performance for the bentonite fluid at higher fluid velocities. It can be concluded that the handling of these drilling fluids is a sensitive task. More rheological analysis is necessary to fully understand the behavior of both fluids. The experiments showed that higher drillstring rotation benefits the hole cleaning. In general both fluids act differently regarding their hole cleaning performance. To investigate what causes these differences, further work could consider to experiment with different sand rates to show the limitations of the sand removal capabilities. Furthermore the gelling properties can be investigated as well as the influence of the air bubbles. Experiments with lower, respectively higher fluid velocities could give information about the variances of the two fluids during the sand bed hold up tests.

KW - Bohrspühlung

KW - Tiefbohrtechnik

KW - Bohrtechnik

KW - drilling

KW - drilling fluid

M3 - Master's Thesis

ER -