**5. Early kick detection and automatic control in managed pressure drilling**

The need for early kick detection systems is further underscored in the implementation of Managed Pressure Drilling (MPD); an adaptive drilling process that enables fast and precise control of the annular pressure profile throughout the wellbore during drilling and completion operations. The accurate monitoring of flow and pressure conditions in the well is achieved due to the closed-loop circulation system (as compared to conventional drilling with an open annulus). Influx and loss situations are detected earlier in systems where MPD is employed as compared to conventional drilling. With MPD the safety of personnel onboard the rig is enhanced since a gas kick circulated with drilling fluid to the surface through the mud-gas separator without either reducing the BHP or stopping the pumps. The risk of sticking pipe is reduced as a kick can be handled without rotating the pipe [34]. Any influx into the wellbore during MPD will be safely contained to avoid continuous influx of formation fluids. Thus, the emergency well control requirements may not be required as the MPD system is set up for its occurrence. MPD has found wide applicability in projects with technical complexity and narrow pressure windows thus enabling the continuation of operations which would have been adjudged unfeasible [35]. The application this technology (MPD) has been shown to achieve automated dynamic well control as well as reduced non-productive time by allowing influx circulation at full rate. It removes human factors intrinsic in conventional well control and the need for flow check, making the need for shutting in the well and consequently the use of the BOP optional [36].

There are three fundamentally different MPD variants implemented based on the operating conditions with different objectives regarding pressure control and influx management. First, Constant Bottomhole Pressure (CBHP) method, BHP is controlled by continuous automatic adjusting of the choke to track the pre-defined pressure profile to eliminate any kick or fluid loss in a relatively unknown and narrow drilling margin. Then, the Dual Gradient Drilling method is used in offshore operations where the return mud does not travel through a large diameter drilling riser as the method reduces the number of casings required. The pressure gradient below the mudline is isolated from the drilling mud gradient above removing the impact of

#### *Advances in Well Control: Early Kick Detection and Automated Control Systems DOI: http://dx.doi.org/10.5772/intechopen.106800*

the water depth on the drilling operations. Third, the Pressurized Mud Cap Drilling method entails the use of a sacrificial fluid like water to manage the mud losses in the highly depleted formation. Of these three MPD variants, the CBHP is the most common variant adopted for drilling in deep offshore environments [14]. The implementation of MPD systems can be considered based on the control parameter such as surface backpressure (SBP), fluid density, fluid rheology, annular fluid level, circulating friction and hole geometry of which SBP is the most used control parameter [34].

MPD-CBHP is typically achieved through a rotating control device (RCD) installed on the surface or subsea BOP to seal the annulus from the atmosphere and closing around the drill pipe. The returns from the well are diverted from the rig floor through a choke manifold while allowing for both pipe rotation and reciprocation. Thus, tripping and drilling operations can be performed while the returns are diverted through the choke manifold. The SBP which is propagated throughout the annulus is used to control the BHP to a desired setpoint by manipulation of the choke openings [34, 35, 37]. The MPD choke manifold is installed separately in parallel with the rigs main flow line and the conventional rig choke manifold. This set-up makes allowance for circulations through the MPD manifold and circulations by conventional methods [35]. The RCD is not considered as a well barrier as regards well control operations [38]. In floating drilling rigs, the RCD is installed below the slip joint with flow diverted through flexible lines to the return system. With this setup, the effect of the rig heave on the circulating volume in the riser is canceled, thus, this remains [5]. The automated choke manifold is run on control systems with a programmable logic controller which could be set to control the valve percentage opening and closing. In addition, the automated choke manifold is connected to auxiliary mud or nitrogen pump to provide the surface back pressure (SBP), as well as monitor flow rates in and out of the wellbore [38]. MPD systems also includes a backpressure pump, flowmeter, and software algorithm. The equipment layout depends on whether the system is manual requiring an operator to control annular pressure via opening and closing of the choke valve, semi-automatic for which the choke is automatically adjusted to obtain the predetermined surface pressure using hydraulics software and automatic requiring a PLC which is programmed with hydraulics software connected to the choke and the backpressure pump that controls the desired annular pressure automatically [5]. A MPD system is illustrated in **Figure 3**.

This dynamic well control method (MPD) is only applicable for influxes up to a certain volume as the kick tolerance (the maximum influx volume that can be handled and safely circulated out of the well) could be as low as 10 bbl (1.590 m3 ) in some deep offshore wells. This necessitates early kick detection via flow measurements. In general, MPD systems provide EKD by using comparison of flow out (return flow) to flow in as a primary kick indicator i.e., delta flow. Coriolis flowmeters are applied for precise monitoring of both flow into the wellbore and flow out with high accuracy. Early gas detection can be achieved by monitoring the annular pressure along the wellbore with pressure sensors mounted at different depths and transmitted via WDP. Replicator stations are used for boosting the pressure signals transmitted along the WDP [5, 35]. A Venturi channel is typically used after the choke controller before the return flow line for flow out measurements towards EKD [39].

Although the level of automation in the different MPD systems varies, an automated response can be initiated to a kick scenario with a fully automated choke that includes a kick detection algorithm. When the MPD system automatically detects an influx, it can respond by increasing the backpressure which actively increases the BHP, accelerating the end of the influx cessation over a passive shut-in response.

**Figure 3.** *A schematic of a MPD system [27].*

In this way, an automated MPD system can reduce kick severity by increasing kick detection resolution thereby reducing inflow time and consequently volume, continual circulation during initial response, maintaining annular friction and preventing a decline in BHP thereby minimizing influx flow rate and volume, and increasing the BHP through active choke manipulation thereby reducing the time to end of influx and overall kick volume. This system provides real time comparison to modeled controlled conditions and automated well control response and signals the driller for necessary actions when specified thresholds are exceeded [6].

The design of pressure control systems for MPD drilling operations requires accurate modeling of the system hydraulics. However, accurate modeling of drilling systems implies to use of highly complex models involving parameterized, nonlinear, nonconservative hyperbolic Partial Differential Equations (PDEs) completed by nonlinear and implicit boundary conditions. These model features render its numerical simulation computationally expensive and make the controller design cumbersome. Model order reduction techniques have been proposed for the construction of models that combine reduced complexity with high predictive capacity. A reduced bias method capable of handling localized nonlinearities has been applied for the modeling of well dynamics under MPD [40]. An alternate approach, the use of real-time high fidelity flow modeling approximates the results of offline complex PDEs but relaxes the model accuracy during the transient phases by assuming a fixed temperature profile and the linear Bingham Plastic model [41]. These hydraulic models are implemented in the controller. Model-predictive control (MPC) techniques which utilize knowledge about the wellbore dynamics and monitored parameters on the rig to compensate for measured changes are adjudged the most appropriate for

MPD operations. MPC techniques have been found superior to simple Proportional-Integral-Derivative controllers [34]. Proper tuning of the automated MPD control systems is necessary to minimize challenge of instability of a non-robust control system of which oscillating choke position is a sign [6]. The difficulty in handling flow-in changes with high precision is also addressed by a robust MPC system [34]. Automated control during MPD is achieved by implementing reduced order high fidelity flow models within an optimal MPC framework.
