Drilling system and method

Abstract

A closed-loop drilling system and method of drilling oil, gas, or geothermal wells is described, whereby through the control of the flow rates in and out of the wellbore, and by adjusting the pressure inside the wellbore by a pressure / flow control device installed on the return line, surface pressure being increased or decreased as required, this in turn decreasing or increasing downhole pressure, occurrence of kicks and fluid losses may be greatly minimized and quickly controlled. Through the method of the invention the elimination of the kick tolerance and tripping margin on the design of the well is made possible, since the pore and fracture pressure will be determined in real-time while drilling the well, and, therefore, nearly no safety margin is necessary when designing the well, reducing significantly the number of casing strings necessary. The inventive method can be called intelligent safe drilling since the response to influx or fluid loss is nearly immediate and so smoothly done that the drilling can go on without any break in the normal course of action. The new method is applicable to the whole wellbore from the first casing string with a BOP connection, and it can be implemented and adopted to any rig or drilling installation that uses the conventional method with very few exceptions and limitations. The new method is applicable to all types of wells, onshore, offshore, deepwater and ultra-deepwater, with huge safety improvement in difficult drilling scenarios.

Description

[0001] The present invention deals with a closed-loop system for drilling wells where a series of equipment, for the monitoring of the flow rates in and out of the well, as well as for adjusting the back pressure, allows the regulation of the out flow so that the in and out flows are constantly balanced at all times. A pressure containment device keeps the well closed at all times. Since this provides a much safer operation, its application for exploratory wells will greatly reduce the risk of blow-outs. In environments with narrow margin between the pore and fracture pressure, it will create a step change compared to conventional drilling practice. In this context, applications in deep and ultra-deep water are included. A method for drilling, using said system, is also disclosed. The drilling system and method are suited for all types of wells, onshore and offshore.BACKGROUND INFORMATION[0002] Drilling oil / gas / geothermal wells has been done in a similar way for decades. Basically, ...

AI Technical Summary

Benefits of technology

[0171] i) accurate and fast determination of any difference between the in and out flow, detecting any fluid losses or influx;

[0188] xvi) to economically drill ultra-deep wells onshore and offshore by increasing the reach of casing strings.

Problems solved by technology

However, in many situations, it can happen that the bottomhole pressure is reduced below the reservoir fluid pressure.

However, if, by any means, the detection of such a kick takes a long time, the situation can become out of control leading to a blowout.

On the other hand, if the wellbore pressure is excessively high, it overcomes the fracture strength of the rock.

In this case loss of drilling fluid to the formation is observed, causing potential danger due to the reduction in hydrostatic head inside the wellbore.

This reduction can lead to a subsequent kick.

This induced well pressure, which by default, is greater than the reservoir pressure causes a lot of damage, i.e., reduction of near wellbore permeability, through fluid loss to the formation, reducing the productivity of the reservoir in the majority of cases.

This technique implies a concomitant production of the reservoir fluids while drilling the well.

In many situations, however, it will not be possible to drill a well in the underbalanced mode, e.g., in regions where to keep the wellbore walls stable a high pressure inside the wellbore is needed.

In this case, if the wellbore pressure is reduced to low levels to allow production of fluids the wall collapses and drilling cannot proceed.

This procedure takes time and increases the risk of blow-out, if the rig crew does not quickly suspect and react to the occurrence of a kick.

Procedure to shut-in the well can fail at some point, and the kick can be suddenly out of control.

In addition to the time spent to control the kicks and to adjust drilling parameters, the risk of a blow-out is significant when drilling conventionally, with the well open to the atmosphere at all times.

However, annular pressure data recorded during kill operations have also revealed that conventional killing procedures do not always succeed in keeping the bottomhole pressure constant.

That is, literature methods are directed to the detection and correction of a problem (the kick), while there are no known methods directed to eliminating said problem, by changing or improving the conventional method of drilling wells.

Also, wells are now drilled in areas with increasing environmental and technical risks.

In this context, one of the big problems today, in many locations, is the narrow margin between the pore pressure (pressure of the fluids--water, gas, or oil--inside the pores of the rock) and the fracture pressure of the formation (pressure that causes the rock to fracture).

In this situation, a reduction in bottomhole pressure, caused by the upward movement of the drill string can lead to an influx.

From FIG. 1, it can be seen that the last phase of the well can only have a maximum length of 3,000 ft, since the mud weight at this point starts to fracture the rock, causing mud losses.

It is not difficult to imagine the problems created by drilling in a narrow margin, with the requirement of several casing strings, increasing tremendously the cost of the well.

Moreover, the current well design shown in FIG. 1 does not allow to reach the total depth required, since the bit size is continuously reduced to install the several casing strings needed.

In most of these wells, drilling is interrupted to check if the well is flowing, and frequent mud losses are also encountered.

In many cases wells need to be abandoned, leaving the operators with huge losses.

These problems are further compounded and complicated by the density variations caused by temperature changes along the wellbore, especially in deepwater wells.

This can lead to significant problems, relative to the narrow margin, when wells are shut in to detect kicks / fluid losses.

The cooling effect and subsequent density changes can modify the ECD due to the temperature effect on mud viscosity, and due to the density increase leading to further complications on resuming circulation.

Thus using the conventional method for wells in ultra deep water is rapidly reaching technical limits.

The industry has mainly taken the direction of the second alternative, due to arguments that well control and understanding of two-phase flow complicates the whole drilling operation with gas injection.

However, there are several technical issues to be overcome with this option, which will delay field application for some years.

The cost of such systems is also another negative aspect.

Potential problems with subsea equipment will make any repair or problem turn into a long down-time for the rig, increasing even further the cost of exploration.

These methods have limited application, i.e., underbalanced and air drilling are limited to formations with stable wellbores, and there are significant equipment and procedural limitations in handling produced effluent from the wellbore.

The underbalanced method is used for limited sections of the wellbore, typically the reservoir section.

This limited application makes it a specialist alternative to conventional drilling under the right conditions and design criteria.

Air drilling is limited to dry formations due to its limited capability to handle fluid influxes.

Similarly Mud-Cap drilling is limited to specific reservoir sections (typically highly fractured vugular carbonates).

This is in contrast to known open well methods which require pausing fluid injection and drilling to unload excess fluid, and add additional fluid, by trial and error until pressure is restored, which can take a matter of hours of fluid circulation to restore levels.

This leads to significant time savings as the traditional approach to dealing with influxes is very time-consuming: stopping drilling, shutting in the well, observing, measuring pressures, circulating out the influx by the accepted methods, and adjusting the mud weight.

Similarly a loss of drilling fluid to the formation leads to analogous series of time-consuming events.

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