An Innovative Fluid Pressure Transmission Pill Successfully Used During Managed Pressure Drilling Operations in an HTHP Environment

Abstract

To successfully perform a Managed Pressure Drilling (MPD) operation in a high-temperature, high-pressure (HTHP) field offshore Norway, an innovative fluid technology was developed for well control purposes. The drilling fluid used in MPD mode had insufficient density for tripping operations. To balance the reservoir pressure when tripping, an isolation pill was spotted in the upper part, leaving dense fluid on top of the well and making the total hydrostatic pressure in the fluid column sufficient for well control. This development pill enabled pressure to be transmitted to the bottom of a well by placing the pill in between a dense fluid on top of a less dense fluid. The design and properties of this pill made it possible to run test wireline logs and eventually a test liner run through the pill, and at the same time, maintain a pre-determined hydrostatic pressure to keep the well under control without externally applied pressure. In addition, the pill did not cause instability by interfacing different density fluids as this would have a dramatic impact on the hydrostatic pressure. One of the criteria was to displace the pill out of the well by using the circulating system only. As this paper describes, the pill stayed intact during the entire operation and displacement of the pill from the wellbore was performed successfully. Another benefit observed was the lack of remedial treatment needed at surface when the pill was circulated out. As this was a solids-free pill, no additional treatment was required. This paper describes in detail the development of the fluid pressure transmission pill and the purpose of using such a pill, including testing performed, and the final result of using the pill for the first time in a well exposed to open reservoir. Introduction A Fluid Pressure Transmission Pill (FPTP), also known as a "Balanced Mud Pill", was developed for use in logging and completion operations during Managed Pressure Drilling (MPD) operations in the Kvitebjørn field. MPD operations have gained popularity for development of modern HTHP gas fields. Batch drilling of entire fields is a high risk and big cost approach. However, due to the rapid pressure drop common in many gas reservoirs after the initiation of production, the pressure regimes for drilling the remaining wells in the project are more challenging. The specific background for the development was well 34/11-A-13 T2 in the Kvitebjørn field. Density for the tests was chosen at 1.87 SG, which was the predicted fluid density while drilling in MPD mode. Required equivalent mud weight to balance the reservoir pressure was estimated to be 1.91 SG and the plan was to use 2.08-SG Cs-Formate mud above the FPTP to achieve this density. The primary target for the project was to develop a crosslinked polymer pill with sufficient integrity to isolate the highdensity brine or drilling fluid in the upper section of the well from the lighter fluid in the deeper section. This would save the cost and logistic challenges of having to displace the entire circulating system to balance the reservoir pressure. The FPTP should also serve as a contingency plan if it should become necessary to open the choke to pull out of the hole without having to displace the entire well volume; thus the pill should be able to transmit the hydrostatic pressure of the added high-density fluid above to the open hole below. The pill should provide sufficient flexibility to enable tripping, allow logs to be run, and finally enable running of liners/production screen assemblies and yet not allow the high-density fluid to channel through it.

Gel Pills for Downhole Pressure Control during Oil and Gas Well Drilling

“…Both the successful gel systems presented in this work are particle gels. Earlier, a crosslinked polymer gel system provided similar effect, as shown by Ronaes et al [25]. In this case, the gel did not bond to hole walls.…”

Managed Pressure Drilling, Casing and Cementing Enables Success in Conventionally Undrillable Wells in the Harding Field

“…The effect of reservoir depletion on in-situ stresses and mud weight selection is discussed in Meng & Fuh (2010) ii . Sand-shale interfaces at the margins of the reservoir, and sand-sand interfaces created by the injection of sand through the main reservoir body also appear to result in localised fracture gradient reduction.…”

“…An auxiliary pump is usually used to provide flow through the choke, enabling control of the SBP when there is insufficient flow from the mud pumps, particularly during connections. A description of the standard setup of an automated MPD system can be found in van Riet et al (2003) iii , for example.…”

“…Key factors to consider in the planning of MPD wells are discussed in Spriggs & Frink (2008) v . The system required the capability to perform casing, liner and completion sand screen running under MPD conditions.…”

“…The design of the MPD system was therefore based around a goal of maintaining ± 50psi from the set-point, allowing a further margin for other sources of error. A simplified hydraulics model for estimation of downhole pressure for an MPD control system is discussed in Kaasa et al (2012) vi .…”