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This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 151392, "An Improved Dynamic-Well-Control Response to a Gas Influx in Managed-Pressure-Drilling Operations," by William Bacon, SPE, Blade Energy Partners; Albert Tong, University of Texas at Arlington; and Oscar Gabaldon, SPE, Catherine Sugden, SPE, and P.V. Suryanarayana, SPE, Blade Energy Partners, prepared for the 2012 IADC/SPE Drilling Conference and Exhibition, San Diego, California, 6-8 March. The paper has not been peer reviewed.
Managed-pressure drilling (MPD) offers the capability to control an influx dynamically, without shutting the well in conventionally. Some current methods use applied backpressure (ABP) to restrict the flow exiting the annulus to equal the flow entering the drillpipe, which is interpreted as influx cessation. However, ensuring only flow continuity does not imply influx cessation, unless the annular fluids are incompressible. This work investigated the effect of compressibility on dynamic well control. The transient response of compressible multiphase flow in the annulus was examined by use of mass conservation over a control volume. Introduction
MPD is a class of techniques that enables management of the annular-pressure profile through a combination of controlling the wellhead pressure (WHP), or backpressure, and the drilling-fluid density and flow rate. With the ability to manipulate backpressure, MPD can be used to control an influx without shutting in the well. Performing well control without conventionally shutting the well in is referred to here as dynamic well control. Well control in MPD operations, dynamic or otherwise, must be performed with several objectives in mind. The most important objectives include minimizing peak WHP and surface flow rates, managing wellbore pressures tightly within the pore-/fracture-pressure window, maximizing the chance of successful well control, and reducing nonproductive time.
When an influx is detected during MPD, one of the most important decisions is whether dynamic well control should be used to control the well rather than conventional well control. Dynamic well control is applicable up to only a certain size and rate of influx, such that the influx can be controlled and circulated out of the system safely and effectively while achieving all of the objectives stated previously. Particularly important is quantifying peak surface flow rates and the point at which it would no longer be safe to shut in conventionally. However, when used appropriately, dynamic well control allows more-rapid control of an influx.
A method based on an approach by Hurst is developed for calculating water influx behavior. Using this method, superposition calculations may be eliminated. The principal difference between this method and that of Hurst is that, over finite intervals of time, constant oil-production rates are assumed by Hurst whereas constant water influx rates are assumed in the presently described method.
By adopting the assumption of constant water influx rate for finite time periods, a method is developed for calculating water influx behavior which lends itself to convenient combination with the material balance equation in the Schilthuis form. Above the bubble point, an equation is given for the explicit step-wise calculation of pressure history for a prescribed oil-production history. Use of this method of calculating water influx behavior should result in a considerable saving of time as compared to superposition calculations when the calculations must be made without using a digital computer.
The connection is shown between the method described herein and the method developed by van Everdingen and Hurst (which requires superposition calculations). Also, results obtained using the two methods are compared.
While the method of van Everdingen and Hurst is in many respects a satisfactory way of calculating water influx behavior, the superposition calculations involved make it a tedious procedure when the work is done without using a digital computer.
Hurst has presented an approach to the problem which eliminates superposition calculations, in many cases at small expense to accuracy. It is the purpose of this paper to present a method of calculating water influx which is based on the approach of Hurst and which may be conveniently combined with the material balance equation in the Schilthuis form. The relation will be discussed between the method of van Everdingen and Hurst and the method described herein. Examples of results using the two methods are given.
Managed Pressure Drilling (MPD) dynamic influx control techniques offer substantial advantages over conventional well control, including reduced influx size, and the ability to control and circulate an allowable influx without requiring conventional methods. With careful planning and execution, MPD dynamic influx control can yield considerable increases in safety and efficiency. Many issues with conventional well control, particularly in deepwater operations, can be mitigated or even eliminated using dynamic influx control. Notably, conventional methods passively rely on the influx to increase wellbore pressure sufficiently to balance reservoir pressure, resulting in needlessly large influx volumes. In contrast, MPD methods quickly detect and actively apply pressure to control an influx in a fraction of the volume. Furthermore, conventional influx removal methods are typically slow, leading to drawn out well control events with high likelihood of further complication, such as stuck pipe and secondary influxes. Conversely, using dynamic influx control, an allowable influx may be controlled and removed from the wellbore in a few hours, not days. In this work, methods that address concerns with current well control practices through application of dynamic influx control are outlined. In addition, transient, multiphase simulation is used to demonstrate comparison between dynamic influx control and conventional well control, clearly quantifying potential benefits of adopting these new methods.
The water influx into a water-drive field may be determined in principle by two essentially independent relationships: the material-balance equation and the diffusivity equation. Direct adaptation of the latter to practical engineering problems is usually precluded, however, because of the general lack of specific information concerning aquifer properties. Upon application, it is found that the diffusivity equation requires the introduction of three aquifer parameters, before water in flux can be computed. These involve the size of the aquifer, its mobility, and a characteristic constant.
The purpose of this paper is to indicate a method for estimating these aquifer parameters from an investigation of the reservoir performance of the associated oilfield. To achieve this objective an analysis was made of the simultaneous solution of the material-balance and diffusivity equations, followed by an application of the method of least squares. As a result, three dimensionless functions were derived for closed, limited, radial reservoir systems: the cumulative fluid influx (taken from the classical work of Hurst and van Everdingen), the rate of fluid influx, and the radial derivative (which is entire novel).
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 185289, “Case Study: First Experience of Developing an Influx-Management Envelope for a Deepwater MPD Operation,” by O.R. Gabaldon, P.R. Brand, M.S. Culen, I.U. Haq, R.A. Gonzalez-Luis, T. Pinheiro Da Silva, G. Puerto, and W. Bacon, Blade Energy Partners, prepared for the 2017 SPE/IADC Managed Pressure Drilling and Underbalanced Operations Conference and Exhibition, Rio de Janeiro, 28–29 March. The paper has not been peer reviewed.
The influx-management-envelope (IME) concept is an advanced, innovative way to assess influx conditions in managed-pressure-drilling (MPD) operations, offering an improved tool for the decision-making process. The complete paper presents the process of developing the IME concept for a deepwater MPD operation for the first time.
The IME Concept
The IME concept defines the operational envelope in case of incidental influxes during MPD operations. It is based on kick-tolerance concepts, in which a relationship between volume and intensity of the influx is established and plotted as a graph. A resulting combination of regions within the volume-and-intensity graph depicts the conditions in which an influx can be removed safely from the wellbore by use of the elements of the primary wellbore barrier; otherwise, the secondary wellbore barrier should be engaged and the well shut in conventionally. The regions are color coded for ease of identification during the process of managing an influx. Three regions have been described:
The Orange Region. In this work, an additional (optional) Orange region is added as a subset of the Yellow region (Fig. 1). In the Orange region, an influx can be removed safely within the primary wellbore barrier but one or more parameters will need to be modified to avoid exceeding some limits in the process.