The 2001 SPE annual technical conference and exhibition, in New Orleans last month, highlighted 32 technical papers on various aspects of drilling technology.
The papers were presented in technical sessions on well control and hole cleaning, development and field test of a dual-gradient drilling system, advancements in drilling fluid technology, cementing and underbalanced drilling, innovative technology in deepwater drilling, effective prevention and mitigation of drilling problems, and drilling optimization technology.
Well control
Pemex Exploration & Production, a unit of Petroleos Mexicanos, controlled a blowout of the offshore Cantarell 69-I well that was drilled into the field's gas cap in just 11 hr after the drillers had taken the initial gas kick.
C. Osornio Vasquez, H. Castro Martinez, V. Vallejo Arrieta, and E. Ayala Vivanco of Pemex presented their work of applying both momentum and dynamic kill procedures to control the blowout.
Crews killed the well by pumping seawater at 19 bbl/min through the 9 5/8-in. x 13 3/8-in. annulus, to the tubing tie-back at 680 m. Due to the well's flowing conditions, the rig could not control it through the 95/8-in. tubing string.
Engineers succeeded with the kill procedure when the flowing pressure at the depth of the tubing tie-back became greater than the reservoir pressure, because of the friction pressure losses and the hydrostatic head of the gas and seawater multiphase flow inside the wellbore.
In another paper, S. Stragiotti of Statoil ASA and T. Skeie and C. Kruger of Welltec Well Technologies explained how the operator used a wireline tractor to recover a radioactive source from stuck drill pipe, deploy explosives for backing off the drill pipe, and to punch holes when the drill pipe became plugged.
Engineers activated the tractor over the interval 3,707-4,085 m at inclinations 70-90°.
Dual-gradient drilling
In 1996, a consortium of operators, deepwater drilling contractors, service companies, and a manufacturer discussed potential approaches to riserless or dual-gradient drilling. Their objective was to eliminate some of the casing strings that are often needed in deepwater Gulf of Mexico wells due to the relatively high pore pressure and low formation strength.
K. L. Smith, A. D. Gault, D. E. Witt of Conoco Inc., Houston and C. E. Weddle of Cherokee Engineering, Houston summarized the efforts to deliver dual-gradient drilling technology to the industry.
The paper focused on the efforts of the team to provide a total solution for dual-gradient drilling, which includes both the hardware, as well as the methodology to safely and efficiently use that hardware.
Texaco Inc. is drilling what it says is the first dual-gradient well using the subsea-mudlift drilling system developed by the joint industry project. The Shasta field No. 8 is in 910 ft of water on Green Canyon Block 136 in the Gulf of Mexico.
Ken Smith said, "We have successfully delivered dual-gradient drilling technology. The design is proving to be robust. The procedures are proving to be sound. In our view, it's only going to get better."
J. P. Schumacher, J. D. Dowell, and L. R. Ribbeck of Texaco Inc. and J. C. Eggemeyer of Conoco presented the planning and preparation for the first subsea field test of the full-scale, dual-gradient drilling system.
The authors said the well in intermediate water depth and known pore-pressure environment offers an excellent opportunity for extensive testing prior to the final development and delivery of a dual gradient-drilling system for use in ultradeepwater, beyond 6,000 ft.
J. C. Eggemeyer of Conoco, et. al., presented the design and implementation details of the dual gradient system.
Bob Rose, chairman and CEO of Global Marine Inc. said, "This is the biggest change our industry has seen since we put the BOP on the sea-bed."
Drilling fluids
Many drilling problems result from uncontrollable drilling fluid losses in large fractures that characterize many reservoirs. Excess fluid loss in highly depleted formations is particularly a problem.
J. L. Quintana of Occidental of Elk Hills Inc. and C. D. Ivan and L. D. Blake of M-I Llc. discussed the development of aphron-based drilling fluids to control invasion. The fluid combines certain surfactants and polymers to create microbubbles, known as aphrons, which are encapsulated in a viscosified system.
The aphron-based drilling fluid provides resistance to fluid movement into and through fractured zones, generating a noninvasive and at-bal anced fluid.
The system does not rely on solids to bridge fractures and control fluid leak-off.
Occidental selected the system to drill the highly fractured Miocene sand in its Elk Hills operations near Bakersfield, Calif., because of the fluid's effectiveness in dril ling highly depleted formations.
In a separate paper, B. Herzhaft and C. S. Dalmazzone of Institut Francais du Petrole, Paris explain the potential problem of gas hydrate formation in drilling muds. The consequences of hydrate formation in drilling muds can lead to loss of mud rheological properties, accumulation of hydrate crystals in the mud system leading to plugged lines or well control equipment, and interruption of drilling operations.
The authors applied an innovative method using differential scanning calorimetry (DSC) to determine the thermodynamic equilibrium properties and kinetics of hydrate formation in drilling muds.
DSC can quantify hydrate appearance in several drilling muds, including water-based and oil-based mud systems.
Once the risk of hydrate formation in drilling mud is characterized, operator's can find ways of counteracting the risks.
Underbalanced drilling
A.C.V.M. Lage of Petrobras SA and R. J. Lorentzen, et. al., of RF-Rogaland Research explain real-time interpretation of measured data and operational support for underbalanced and low-head drilling operations.
The authors said, accurately predicting downhole pressures and the returning flow rates in low-head drilling and underbalanced-drilling operations is a major concern for operators.
A dynamic two-phase flow model is coupled with measured data acquired during execution of the operation.
The methods developed are able to update the model parameters and variables of state, to yield reliable predictions for low-head drilling and underbalanced drilling operations.
Deepwater technology
In addition to dual-gradient drilling, the authors raised several other issues regarding deepwater drilling. C. D. Whitson and M. K. McFadyen of Texaco Inc. presented lessons learned in the planning and drilling of deep, subsalt wells in the deepwater Gulf of Mexico.
They pointed out that more deepwater wells are being drilled for subsalt objectives that have 6,000 ft or thicker salt sections and well depths in excess of 25,000 ft.
The advantages of the long salt sections are higher fracture gradients within the salt and the absence of typical well control problems associated with permeable formations. Combined, this allows for longer hole sections between casing strings.
Disadvantages however are the difficulty in predicting the pore pressure and fracture gradient in the sedimentary section below the salt and hole deviation or directional control problems in the salt.
Their paper outlines the approach taken in planning of two wells and discusses the lessons learned during execution. They found that long salt sections can be used to extend casing points and eliminate well control issues.
The authors concluded that conventional, non-under-reaming bits, stablilzed-bottomhole assemblies, and synthetic oil-base mud maximize the rate-of-penetration within the salt.
Also, successfully running heavy, long casing strings requires detailed planning and an effective quality-control program.
