A.T. Bourgoyne

Fracture-Gradient Prediction for Offshore Wells

A key parameter required in the design of offshore wells is the fracture gradient of the formations to be penetrated. Existing fracture-gradient correlations have been developed largely on the basis of empirical data gathered on land and in the near-shore marine environment. They have been extended to deepwater areas through an equivalent intergranular stress concept. In this study, offshore data from several operators were obtained and a new fracture-gradient correlation procedure, based on an assumption of an exponential decline in average porosity with depth in normally pressured formations, was applied. The technique is ideally suited for implementation on a hand-held calculator or personal computer.

Swelling of Oil-Based Drilling Fluids Resulting From Dissolved Gas

The method presented in this paper uses an experimentally calibrated equation-of-state (EOS) model to estimate the swelling of oil-based drilling fluids caused by dissolved methane. With this method, the pit gain associated with a given kick size can be determined. The calculation method was verified by experiments conducted in a 6,000-ft (1828.8-m) test well. Example calculations are also presented.

Frictional Pressure Losses for the Flow of Drilling Mud and Mud/Gas Mixtures

In this study, experimental pressure gradient data have been taken in two 6000 ft. wells. Frictional pressure losses for single phase flow (mud only) in two annuli were compared to values predicted by the Bingham Plastic and Power law Models. These calculations utilized the equivalent diameters defined by the Crittendon criteria, the hydraulic radius, and the slot approximation. Also, total pressure difference for two-phase flow was measured for one annular geometry. This data was compared to that predicted by the Poettmann and Carpenter, Hagedorn and Brown, Orkiszewski, and Beggs and Brill correlations. Comparison of experimental data with the various prediction techniques was favorable, each having advantage in certain situations. For the data investigated, the Crittendon criteria using a Bingham Plastic Model gave the best results. The two phase flow data was best predicted by the Hagedorn and Brown correlation utilizing a hydraulic radius equivalent diameter.

A Feasibility Study on the Use of Subsea Chokes in Well Control Operations on Floating Drilling Vessels

The use of a subsea remote-operated adjustable choke between the blowout preventer (BOP) stack and the marine riser was considered as a means of eliminating the need for long subsea flowlines. Well behavior was predicted through computer simulations and showed that existing problems could be reduced but not eliminated entirely. 3 refs.

Estimating break-down pressure of upper marine sediments using soil boring data

Abstract This paper illustrates how soil boring data is used to determine the formation break-down pressure for the Green Canyon area of the Gulf of Mexico. Example soil boring data is integrated with deeper well log data to accurately estimate overburden stress. Values for the horizontal to vertical effective stress ratios are confirmed by measuring the actual in situ formation break-down pressure while collecting the soil samples. This study shows that upper marine clays for the Green Canyon Area example have horizontal to vertical effective stress ratios of about 1.0 rather than the extrapolated value of 0.33 often used for sands. The current objective of soil-boring geotechnical studies is to aid in the design of platform foundations. This study recommends that oil-boring geotechnical studies be extended to include obtaining data for designing shallow-gas well control systems.

Shale water as a pressure support mechanism in gas reservoirs having abnormal formation pressure

Abstract One problem often confronting reservoir engineers is an analysis of the reservoir mechanisms involved in the depletion of abnormally high pressure reservoirs. Two mechanisms that have been proposed are: (a) high rock compressibility; and (b) shale water influx. This paper is a study of the shale water influx theory. A literature search was conducted to establish what is known about shale permeability, compressibility, porosity, and water viscoity. The shale properties were used in a calculation of water influx for two actual superpressure reservoirs using a linear diffusivity equation in which permeability and compressibility were a function of pressure. Of the shale parameters, permeability and compressibility have the most influence on water influx. For an initial shale permeability of the order of 10 −5 mD and an initial bulk compressibility of 40 × 10 −6 psi −1 , shale water influx significantly affects the reservoir depletion. For shale permeabilities of the order of 10 −7 mD, shale water influx is insignificant. It was also noted that the pressure distribution in the shale is very steep and only the first few feet of shale contribute materially to the water influx. An approximate method for extrapolating early p / z behavior in superpressure gas reservoirs is also presented.

Experimental Evaluation of Control Fluid Fallback During Off-Bottom Well Control

This study measured the liquid fallback during simulated blowout conditions. The purpose of the study was to establish a basis for developing a procedure for controlling blowouts that relies on the accumulation of liquid kill fluid injected while the well continues to flow. The results from full-scale experiments performed with natural gas and water based drilling fluid in a vertical 2787-foot deep research well are presented. The results show that the critical velocity that prevents control fluid accumulation can be predicted by adapting Turner’s model of terminal velocity based on the liquid droplet theory to consider the flow conditions, velocity and properties of the continuous phase when determining the drag coefficient. Similarly, the amount of liquid that flows countercurrent into and accumulates in the well can be predicted based on the concept of zero net liquid flow (ZNLF) holdup.Copyright

PDC applications in the Gulf of Mexico with water-based drilling fluids

This paper presents the results of a recent study conducted to determine application and operating requirements for Polycrystalline Diamond Compact (PDC) bits in the Gulf of Mexico. This study evaluated PDC bit usage in Miocene sections of the Gulf of Mexico and has resulted in a savings of over

An experimental study of well control procedures for deepwater drilling operations

1.4 MM based on twenty two bit runs. As a result of this study, operational guidelines for PDC bits were established and drilling costs per foot were significantly reduced. In addition, a relationship was found to exist between shale reactivity, strength and density. This proved to be an effective aid in bit selection and determination of hydraulic requirements and verified the results of the study.

Experimental Study of Erosion in Diverter Systems Due to Sand Production

A research facility has been designed and constructed to model the well-control flow geometry present on a floating drilling vessel operating in 3,000 ft (914 m) of water. The main feature of this facility is a highly instrumented 6,000-ft (1829-m) well equipped with a packer and tripleparallel flow tube at 3,000 ft (914 m) to model a subsea blowout preventer (BOP) stack with connecting subsea choke and kill lines. Several types of experiments were conducted in which gas kicks were simulated by the injection of nitrogen into the bottom of the well. Alternative procedures studied and evaluated included techniques to compensate for chokeline frictional pressure loss during pump startup and techniques for handling rapid gas-zone elongation when the kick reaches the seafloor. It was found that the demands placed on a choke operator during well-control operations in deep water were not as severe as anticipated from computer simulator studies and could be managed with existing equipment by an experienced choke operator.