This paper analyzes well control for horizontal wells. It presents a computer model for predicting the pressure behavior in a horizontal well during gas-kick removal and analyzes the simulation results for several field conditions. The paper also analyzes the drillpipe-pressure schedule, the kick-tolerance concept, and the swabbing effect during tripping out of the hole.
An unexpected and unwanted influx of gas or "kick" into the wellbore during hydrocarbon drilling can cause catastrophic blowout incidents, resulting in human casualties, ecological damage, and asset losses. The ability of the oil and gas industry to control gas kick depends on our ability to accurately detect and monitor gas migration in a borehole in real-time. This study demonstrates the application of optical fiber-based Distributed Acoustic Sensors (DAS) for early detection and monitoring of gas in wellbore. Multiphase flow experiments conducted in a 5000 ft. deep test-well are analyzed for different injection, circulation, and pressure conditions. In each case, the low-frequency component of DAS demonstrates a superior capability to detect gas signatures both inside the tubing and the annulus of the well, even at small gas volumes. In comparison, the highfrequency DAS data seems limited in detail. The gas influx velocity was calculated using the frequency-wavenumber analysis of the gradient of the low-frequency DAS phase with respect to time, which shows good agreement with theoretical velocity estimates using flow models and surface gauge measurements. This study demonstrates a novel workflow to analyze low-frequency DAS to qualitatively and quantitatively map gas influx in a wellbore.
Optimization of single bit runs to achieve the minimum cost per meter has been discussed and published quite extensively throughout papers, journals, and other periodicals. Very little has been said and done concerning multiple bit runs that is the case for over 90% of the wells drilled worldwide. The reason for this is that the problem is much too complex to be solved with a set of analytical equations due to the interdependence of some of the drilling model coefficients, the uncertainties associated with the parameters involved such as the rock type, strength and mechanical properties, and a good handle on the historic operating conditions and bit grading. A research program was commissioned to address this based on an heuristic approach to seek the optimum conditions using Monte Carlo Simulation and specially developed numerical algorithms. The output of the program yields the operating conditions for each individual bit run so that the overall cost are minimized for the entire well phase drilled. The method does not depend on a particular drilling model and has been tested with several models such as Bourgoyne & Young's, Warren's and others. The paper shows results of using the first two models mentioned due to their greater acceptance within the very small portion of the drilling industry that uses drilling models at all. The results show an average cost per meter savings of over 10% in most cases and can be as high as 30% depending on the length to be drilled and the number of bits required. Introduction The main objective of this paper is to show that drilling optimization by well phases is more economical than the optimization by single bit runs. To prove that, five different methods of drilling optimization have been studied. The methods that consider the optimization by well phase have shown to be more economical. The results for all five methods of drilling optimization have shown consistency in their predictions. Since the methodology for optimizing bit runs is affected by the drilling rate equation used in the calculations, first in this paper, an analysis of several equations for rate of penetration available in the literature has been carried out. In this analysis, emphasis has been given to two more sophisticated drilling models: Bourgoyne & Young and Warren. Analysis of the Drilling Models A drilling model consists basically of equations for penetration rate and bit wear. Then, the first step of analysis was to study available equations for penetration to verify their fitness to data published by Black et. al. Penetration Rate Equations The penetration rate equations analyzed in this work are as follows: (1) (2) (3) (4) (5) (6) In these equations, Tx is the rate of penetration, W is the weight on bit and N is the rotary speed. To determine the constants (a, b and c) for each model, the Multidimensional Powell's Method and the Brent's Method in One-Dimension were applied. The function to be minimized is as follows: (7) P. 579^
Early detection of a gas kick is crucial for preventing uncontrolled blowout that could cause loss of life, loss of assets, and environmental damage. Multiphase flow experiments conducted in this research demonstrate the capability of downhole fiber optic sensors to detect a potential gas influx in real-time in a 5000 ft deep wellbore. Gas rise velocities estimated independently using fiber optic distributed acoustic sensor (DAS), distributed temperature sensor (DTS), downhole gauges, surface measurements, and multiphase flow correlations show good agreement in each case, demonstrating reliability in the assessment. Real-time data visualization was implemented on a secure cloud-based platform to improve computational efficiency. This study provides novel insights on the effect of circulation rates, gas kick volumes, backpressure, and injection methods on gas rise dynamics in a full-scale wellbore.
The drilling of horizontal wells to improve oil and gas recovery and productivity has quickly become one of the most important and promising technology of the oil industry. This is reflected by the considerable number of technical papers published on this subject. Although these papers have been covered a great deal of aspects of horizontal drilling, one important subject remains almost unexplored: the well pressure control. The scope of this paper is to show important facets of the well control for horizontal wells, especially for deepwater ones, and to highlight some design and operational aspects to make the horizontal drilling safer. One important point analyzed in this paper was the pressure behavior inside a horizontal wellbore during a gas kick removal process. For this analysis, a numerical simulator of a gas kick based on the unsteady state flow of a two-phase mixture (gas and mud) has been developed and used to predict pressure at any point of the wellbore-choke line system. It has also been used to compute and to analyze the kick tolerance during the gas kick circulation process. process. Some other relevant points of the well control operation for horizontal wells that differ from those for vertical wells were also investigated. They include: swabbing effect when tripping out of the hole, shut-in pressures and pit gain, drillpipe pressure pressures and pit gain, drillpipe pressure schedule during the kick removal process, and mud density design. Introduction The potential of horizontal wells to increase hydrocarbon production rates and final recoveries justifies the current importance and worldwide application of them. Though they can be drilled to drain many kinds of reservoirs, including thick, homogeneous and highly permeable ones, they are preferentially drilled to produce thin, naturally fractured and coning problem reservoirs. The importance of this kind of wells may increase when considering the development of an off-shore reservoir that requires high production rates and recoveries to be economically feasible. The importance of this kind of wells is also suggested by the huge amount of technical literature on this topic. Many important aspects of the horizontal drilling have been discussed by a lot of papers published recently. These papers, however, published recently. These papers, however, have given little attention to one of the most important facets of the drilling operations: the well pressure control. One of the few papers on well pressure control in horizontal wells describes a computer model to predict the pressure behavior inside a horizontal well drilled land during the circulation of a gas kick. P. 785
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