Hans C. Juvkam-Wold

Coiled tubing buckling implication in drilling and completing horizontal wells

This paper discusses coiled tubing buckling and load transmission when drilling and completing horizontal wells. Comprehensive analyses and new equations are presented to predict buckling of coiled tubing, slack-off weight transmission, actual bit weight or packer load, and maximum horizontal length. Coiled tubing lock-up and yield due to buckling are also discussed. These equations can also be used for other coiled tubing operations, such as coiled tubing workover, coiled tubing well stimulation, and even for conventional joint-connected drill strings. Calculations based on the equations presented are also compared with the previous literature.

A Modified Two-Phase Well-Control Model and Its Computer Applications as a Training and Educational Tool

This paper presents a modified two-phase well-control model to simulate two-phase kick behavior after comparing a dynamic two-phase well-control model and a single-phase model. The model is reliable and easy to simulate without any of the numerical problems that might occur in a dynamic two-phase model. The simulator calculates gas influx rate from the formation assuming an infinite-acting reservoir. The paper also introduces computer applications for IBM-compatible personal computers for use as a well-control training and educational tool. The simulator has enhanced graphical presentations with random access for all menus and options by use of a computer mouse. The simulator is written in Visual Basic{trademark}3. The simulator can handle vertical wells, directional wells, extended-reach wells, and horizontal wells with two different buildup rates for onshore or offshore wells. The simulator also provides the theoretical kill sheet for any selected well geometry. The simulator is a user-interactive well-control program with an automatic well-control option. It demonstrates the basic concepts of well control and shows the pressure and volume response of the kick with time.

Well Control Aspects of Riserless Drilling

Riserless drilling is a term used to describe an unconventional technique using a relatively small diameter pipe as a mud return line from the sea floor instead of a large diameter marine riser. The scheme also balances internal and external pressures at the sea floor by reducing the internal pressure to make a dual pressure gradient possible. This paper presents basic concepts of riserless drilling and a brief review of problems associated with conventional marine riser drilling for deep water applications. The paper also presents hydraulics, kick detection methods, and well control aspects of riserless drilling with comparison to conventional riser drilling. Other operational considerations are given briefly.

Unconventional Method of Conductor Installation to Solve Shallow Water Flow Problems

In the Gulf of Mexico, in water depths from about 2,000 to 4,000 ft, a number of wells have experienced serious problems with high flow rate shallow water flows from over-pressured aquifers, typically at depths from 400 to 2,000 ft below mud line. The resulting erosion of the wellbore can cause serious borehole enlargement. Continued erosion by the water flows can result in the conductor (or structural) casing losing its support, thereby sliding downwards, causing the next casing or any inner casings to buckle, sometimes resulting in well failure that requires abandonment. One of the potential solutions to shallow water flow problems is to drive the conductor casing(s) to about 2,000 ft below mud line. This paper presents evaluation of the technical feasibility of implementing the above method using wave equation analysis. It also includes evaluation of remolded miniature vane shear soil strength in the Gulf of Mexico for depths down to 2,000 ft below mud line. Cost analysis comparison to conventional drilling procedures is given. The initial objective of driving the 30-inch conductor to a depth of 2,000 ft in one pass is technically feasible but time and cost would be unacceptably high with current technology. In most cases it is possible to drive a 30-inch conductor to a depth of 800 ft below mud line at a cost below half a million dollars. This amount of penetration should provide sufficient support to hang all subsequent casing strings, and to prevent downhole buckling resulting from settling or subsidence.

A Simplified Well Control Model for Horizontal Slimholes and Coiled Tubing Drilling

This paper presents the development of a simplified two-phase well control computer model to simulate gas kicks. The paper identifies key factors in the prediction of kick behavior based on a comparison between a fully implicit dynamic two-phase model and a single-phase model. The model also analyzes kick responses for directional and horizontal slimholes and wells drilled with coiled tubing. Directional and horizontal wells consider multiple build-up rates. This paper highlights the effect of homogeneous or locally high pressured horizontal wells and the effect of reeled coiled tubing. This paper also examines theoretical kill sheets for several well trajectories from vertical to horizontal and for coiled tubing drilling. Theoretical kill sheets are compared with conventional kill sheets. The simplified two-phase well control model developed in this study is reliable and stable. It can handle vertical, directional, and horizontal wells with multiple build-up rates and hold sections and does not have any numerical problems such as may occur with a dynamic two-phase well control model. For directional and horizontal wells with high build-up rates, choke pressure changes rapidly without much kick expansion because of vertical height change of the kick mixture as the kick moves through the curve. A conventional kill sheet is good enough for a conventional large diameter vertical well with uniform well geometry. However, a theoretical kill sheet should be used with some amount of over-pressure for directional, and horizontal wells, especially when those are slimhole wells or are drilled with coiled tubing.