The understanding of kick and gas - oil-based drilling fluid (OBDF) interaction is essential for the planning and operational safety of drilling. The capability to detect gas kick at an early stage and to estimate the gas kick severity is critical.
In this respect the two classes of OBDFs are investigated, one with normal mineral base oil, and the other with linear paraffin base oil. The latter is often used in HPHT drilling applications.
The gas kick detection characteristics is determined by experimental studies of the methane-OBDF equilibrium conditions at pressure and temperature conditions ranging from STP conditions to conditions relevant for HPHT; 200 °C/1000 bar. The OBDF gas loading characteristics is derived from the determination of the two-phase envelope of methane and OBDF. The two-phase envelope towards single phase liquid is determined for selected temperatures and gas mass fraction of methane in the gas-liquid mixture. The equilibrium conditions are studied for both the two OBDFs and the associated classes of base oils; normal mineral base oil and linear paraffin base oil.
It is observed that the maximum methane gas loading capabilities for the two OBDFs are quite similar and follow a linear relation between max gas mass loading in the liquid vs. pressure at pressure below 400 bar. However at higher pressures the performance of the OBDFs differs distinctively, where far more gas can be absorbed in the OBDF with linear paraffin base oil. This OBDF enters into the dense phase region at pressures exceeding 400-450 bar, for which the solubility of gas into the liquid goes to infinity. The dense phase region is encountered at somewhat 100 bar higher with the normal mineral base oil, reflecting fare more attractive characteristics when it comes to the capability for gas kick detection and well control.
The findings illustrate that the selection of base oil for OBDF has an impact on the kick detection capability at HPHT as the gas loading capability and the dense phase region depends on the class of base oil selected for the OBDF. The results also indicate that the operational procedures should be adjusted according to which type of OBDF is used.
The objective of plug and abandonment of wells can be described as "restoring the cap rock". In that respect, the long-term integrity of the plugging material is crucial. I.e. it is important that the plugging material can resist downhole chemicals and otherwise withstand downhole conditions. In this paper, we have performed ageing tests with cement samples at relevant downhole conditions to determine the long-term integrity of well cement as plugging material. Portland cement samples with and without silica flour as additive have been separately exposed to crude oil, brine and H2S (in brine) at 100 °C and 500 bar for 1, 3, 6 and 12 months. The long-term integrity of the samples was determined by measuring changes in weight, volume, mechanical strength and permeability, as well as physical appearance.
It is seen from the results that the addition of a pozzolan such as silica has a significant impact on the long-term integrity of Portland cement, especially in a corrosive environment such as H2S. All the samples were affected by most of the different chemical environments, but the cement samples without silica were considerably more affected than the samples with silica as additive. Furthermore, the exposure to H2S in brine resulted in the formation of an unexpected white deposit, which precipitated both inside and outside the samples.
Al Dushaishi, M. F. (Missouri University of Science and Technology) | Nygaard, R. (Missouri University of Science and Technology) | Andersen, M. (National Oilwell Varco) | Jeffery, C. (National Oilwell Varco) | Hellvik, S. (National Oilwell Varco) | Saasen, A. (Det Norske Oljeselskap and University of Stavanger) | Hareland, G. (Oklahoma State University)
To avoid severe vibrations, different drillstem (or drillstring) vibration models have been used to predict and avoid resonance regions by selecting bottom hole assembly (BHA) components and operating parameters such as weight on bit (WOB) and RPM. The overall efficiency of the drilling operations can be evaluated using either a mechanical specific energy model or an inverted rate of penetration (ROP) model. The key output from the analysis described herein is a method to improve drilling efficiency by incorporating a drillstem vibration model with an ROP model.
A data set including vibrational data was collected from a section of a well drilled in the North Sea to analyze the level of drilling efficiency for the drilled section. A drillstem vibration model was created using nonlinear finite strain theory, including coupled axial, torsional and lateral vibration modes. To optimize the drilling process, the vibration model was integrated with an ROP model. The vibration model calculates the critical speeds for a given BHA at a given depth, supplied with an operational window for WOB and RPM combinations that gives the optimal combination in therms of ROP.
By analyzing the drilling variables such as WOB, rotational speed, and ROP, the drilling operational effectiveness was evaluated. The operational window with low vibration level and with the potential maximum instantaneous ROP was chosen to be the optimum drilling scenario for the target hole section. The model was verified with the analysis of the collected field data where the level of drilling efficiency was obtained for the different sections drilled. This paper presents a new methodology to increase drilling performance by means of drillstem vibration and ROP modeling.
Stokka, Sigmund (IRIS) | Cayeux, Eric (IRIS) | Gardner, David (IRIS) | Kragset, Steinar (IRIS) | Lohne, Hans Petter (IRIS) | Randeberg, Erlend (IRIS) | Skadsem, Hans Joakim (IRIS) | Aas, Bjarne (IRIS) | Kyllingstad, Henrik (Hole in One Producer) | Larsen, Torgeir (Wintershall) | Saasen, Arild (Det Norske Oljeselskap and University of Stavanger)
Current Extended Reach Drilling (ERD) well technology limits the well lengths to roughly 12 km with a horizontal departure of approximately 10 km. This paper presents a concept that enables simultaneous drilling and completion with an aim to substantially extend well reach and with an ultimate objective of constructing 30 km long production wells. Longer reach wells can be used to drain remote reserves using existing production facilities, as well as provide a means to access reservoirs located beneath environmentally sensitive areas.
The key technology elements that enable the concept to construct long reach wells are multiple sliding packer traction units in combination with a dual casing drilling system, comprised of a casing with an inner tubing. The sliding packer traction units provide two primary functions; continuous well control along the length of the borehole and traction to overcome axial friction. In addition, the traction packers provide a stable bottom-hole drilling platform avoiding the occurrence of drilling instabilities such as stick-slip, which can damage conventional bottom-hole assemblies and the drill bit in particular. The dual casing provides the conduit for drilling fluid circulation to the bit and cuttings transport to surface. The drilling fluid is pumped through the annulus formed between the casing and inner tubing. The drill cuttings are transported to surface through the inner tubing, ensuring efficient cuttings transport with a low-pressure loss.
The concept has been developed through a five-year project, kicked off in 2010. A prototype has been built and tests have shown that each sliding packer traction unit is able to push the drill bit or pull a completion string with a large axial force in excess of the estimated requirement. In the paper, elements of the system are described in detail and the results of the full-scale yard tests are presented.
The concept represents a new well construction method incorporating advanced completion technology. It enables drilling and completion of long reach wells and can operate in areas with complex pressure regimes, such as can occur from pressure depletion due to production or pressurizing as a result of the injection of water or gas. Well control is provided by packers placed in pairs that seal off the annulus at predefined intervals along the drill string. Production takes place through a large inner diameter. It is a well construction method with no flat time.
Khalifeh, Mahmoud (University of Stavanger) | Hodne, Helge (University of Stavanger) | Korsnes, Reidar I. (University of Stavanger) | Saasen, Arild (Det Norske Oljeselskap and University of Stavanger)
The fundamental of a plug and abandonment operation is to restore cap rock functionality for securing the well-integrity permanently. The current work reviews briefly essential characteristics of plugging materials. Besides, since geopolymers have been suggested as a possible well barrier element, rheological behavior and mechanical properties of a rock-based geopolymer is presented. The consistency and viscosity of different mix designs were investigated to study the placeability of the mixes. Although the slope of the acquired viscosity data may show a Newtonian fluid behavior, a non-Newtonian model (Herschel-Bulkley) simulated the experiments with a lesser deviation than the power-law model. Strength development of the produced geopolymers showed sufficient strength. Confined triaxial compression tests were performed to measure the Bulk modulus, Poisson's ratio, E-modulus and Young's modulus at downhole conditions. Very low Young's modulus (238 Kpsi) and Poisson's ratio (0.01) were measured. The setting time of the mixtures was delayed by using sucrose without compromising the right-angle-set. The use of sucrose as a retarder by 1.9 w% of the total solid phase did not affect the mechanical properties. SEM analysis showed some unreacted aplite particles within the geopolymers. The initial results showed that the rock-based geopolymer has the potential to be utilized as a well barrier element for permanent well plugging and zonal isolation.
Khalifeh, Mahmoud (University of Stavanger) | Saasen, Arild (Det Norske Oljeselskap and University of Stavanger) | Vrålstad, Torbjørn (SINTEF) | Larsen, Helge B. (University of Stavanger) | Hodne, Helge (University of Stavanger)
When a well reaches the end of its life-cycle, it is permanently plugged and abandoned. Since the first discovery in 1966 on the Norwegian Continental Shelf (NCS) till October 2014 nearly 5496 wells have been drilled. Of these wells, 3978 are development and 1518 are exploration wells. Of the development wells, 699 have permanently been abandoned and 279 are in temporary abandonment status. It is estimated that 3279 development wells need to be plugged and abandoned in the future. Besides, the number of wells which will be drilled in future should be added for plug and abandonment.
The costs of these P&A operations will be substantial. Hence, there is a need for technology development that will reduce the costs of all these operations. This development involves both techniques, tools and materials. The current work describes different plugging materials and important characteristics of permanent barriers with respect to long-term integrity. In addition, different roots of failure modes of permanent barriers have been discussed. Geopolymers are suggested as possible permanent plugging materials. Geopolymers are aluminosilicate materials, which solidify. A new geopolymeric material is introduced for the permanent zonal isolation and well plugging; an aplite-based geopolymer. Its placeability was studied by investigating the rheological behavior of the geopolymer slurries. The Bingham and Casson models selected to simulate the slurries' viscosities. Both models were fitted to the measured data. Strength development of the produced geopolymers showed sufficient compressive strength. X-ray powder diffraction was used to characterize the microstructure of the produced geopolymers. X-ray patterns showed formation of an amorphous phase. The measured permeability was in the range of nano Darcy. The initial result shows that the aplite-based geopolymer has the potential to be utilized as a permanent plugging material for well plugging and zonal isolation.