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8/19/2019 NDTbkpngENG

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PNG Drilling Company: New Drilling Technologies


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New Drilling Technologies Reducing Risks of Wellbore Integrity Loss: MPD & CCS

Introduction

One of the important aspects of oil & gas well drilling is early prevention of troubles related to kicks

or losses during bore hole drilling.

Such troubles are caused by undesirable depressions (or repressions) arising in the course of

drilling as result of mud bore hole column pressure excess or reduction against reservoir pore

pressure.

Such situation may take place in the following cases:

• bore hole mud column height drops as a result of catastrophic mud losses;

• loss of borehole fluid column weight resulting from gas kicks onto the well;

• mud flowing pressure decrease (during tripping operations, forced downtime caused by

drilling equipment failure etc.);

• over-balanced or under-balanced well completion;

• mistakes in forecasting (calculating) formation (pore) pressures, loss and fracture

pressures (drilling conditions compatibility zone identification) etc.

Today, to prevent the above complications traditional methods are used: mud weight (density)change using chemical additives, running intermediate casing strings for incompatible formation

isolation etc. However, such conventional methods require, on the one hand, considerable non-

refundable tangible costs, on the other hand, those methods lack operational flexibility as, e.g.,

mud weighting up or weight reduction require time and considerable labor input. Moreover, it is not

always possible to overcome complications arising in the course of drilling solely by means of mud

control, sometimes this is not sufficient.

PNG Drilling Company offers efficient additional technologies and tools of the said problem

solution based on best international practices and know-how of complicated well drilling including

but not limiting to offshore drilling.

The key point of the offered technologies is the use of dedicated non-conventional wellhead

equipment set, complex design manifolds, special drill pipe subs and software. It should be noted

that PNG DC technologies do not replace but rather complement operator or contractor outfit with

new highly efficient means for complicated well drilling.

PNG Drilling Company offers 2 (two) new techniques that may be used both jointly and separately

from each other:

• Managed pressure or underbalanced drilling (hereinafter – "MPD")


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• Mud continuous circulation system (hereinafter – "CCS").

The offered techniques have been developed by PNG DC jointly with European equipment

manufacturers and have foreign analogues (NOV, Aker Solutions, ENI, Halliburton, Schlumberger,

Weatherford, MPO Companies), the said analogues being mainly applied in offshore drilling (Gulf

of Mexico and Persian Gulf, Caspian, North and Mediterranean Seas).

Application of the offered technologies enables to essentially mitigate risks of well control loss in

the course of drilling and the related therewith secondary risks. At the same time, the said

technologies are cheaper than traditional solutions and techniques applied in Russia.

Fig. 1 below presents schematically our MPD and CC systems' allocation on drill site. The blue

lines represent high pressure (HP) delivery line from mud metering tank to vertical manifold andtop drive (mud circulation great circle). Green lines show HP delivery line branch from complex

design manifold to CCS hydraulic power arm, see Fig. 4 below (mud circulation minor circle). Black

lines show return line from rotating BOP to Circulation System through mud gas separator (optional

- on request).

MPD and CCS functioning logic is presented herein below.

Schematic presentation of well inlet and outlet lines, choke controllers, other monitoring systems

including MPD and CCS control panels are shown in the diagram (see Fig. 3 below).

Fig. 1. Drilling rig simplified schematic with new system and techniques' elements


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Brief Technology Description

1. Managed Pressure & Underbalanced Drilling (MPD)

This technique application is recommended for drilling in the so-called narrow window zones when

gradient curves of formation (pore) pressure (Ppore), mud pressures (Рmud) and fracture pressures

(Рfr.) are close to each other (see Fig. 2 below).

Fig. 2. Evseevsky Field (Pre-Caucasian region) Geological & Technical Conditions and Exploration

Well Design

In such conditions, insignificant variations of mud density may cause either mud loss (Рmud > Рfr.) or

oil/gas/water kicks (Рpore > Рmud).


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This refers also to situations when it is difficult to forecast the presence and/or characteristics of

narrow drilling window zones because of insufficient geological data of drilling concession area.

Traditionally in such situations the first thing to do is to try to change mud weight/density (reducing

weight or weighting up) in order to balance pore pressure and well column mud pressure.

However, this requires additional time and, as experience has proven, sometimes it is too late to

take such measures. Then you have to stop drilling and deal with complications. There is high risk

of serious accidents.

The offered by PNG DC MPD technique uses dedicated sensors enabling every single moment to

monitor mud (a) density, (b) temperature and (c) flow rate in and out and to provide contractor with

corresponding information in on-line mode (Fig. 3 below).

Fig. 3. Diagram of wellhead equipment when using MPD technique

Contractor is informed of loss or kicks in well within less than one minute from the corresponding

event occurrence.

Dedicated electronic adjustable wellhead choke (located downstream of rotating BOP) enables

drilling contractor to adjust outlet well choke (from 0 to 100% opening).


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In this way, drilling contractor has the possibility to change immediately bottom hole pressure by

means of (i) fully opened inlet valve (delivery line manifold), on the one hand, and (ii) partly closedby choke regulator outlet valve, on the other hand. The difference between mud flow rate in and

out creates fluid column adjustable hydrodynamic pressure onto open bore hole and onto bottom

hole.

2. Mud Continuous Circulation System (CCS)

Even short interruption of mud circulation may cause potential geological complications in the

course of drilling.

In drilling practice, forced interruption of mud circulation, as a rule, takes place during tripping

operation performance. Even when drilling using top drive, in the course of making up or breakingin connection, circulation may stop for up to 10 minutes and more. In case of top drive breakdown,

swivel failure, circulation may stop for a longer time.

Requirements to bottomhole cleaning process and mud circulation are even much more stringent

in offshore drilling. A wellbore left without mud circulation for 10 minutes and more, is subjected to

serious risk of caving-in, borehole wall collapse, tool sticking and even well control loss.

In current Russian drilling practice there are no industrially tested methods ensuring continuous

mud circulation.

Continuous circulation technique enables drilling contractor to provide uninterrupted mud

circulation without stopping to make up connections or to perform tripping operations.

CCS comprises:

• complex design manifold with control station and control panel,

• hydraulic power arm mounted on a pedestal on drilling floor with a dedicated jaws to catch

DP and mud insulation packer (see Fig. 4),

• Dedicated subs with valves screwed on every DP or DP stand (see Fig. 4 below).

Depending on the type of operation being performed (well drilling or tripping), CCS directs mud

flow via complex design manifold from mud pumps along (A) great circle (see Fig. 1 – blue color)

or along (B) minor circle (see Fig. 1 – green color).

(A) great circle circulation (blue lines in Fig.1) is effected during well deepening via complex design

manifold to the top drive (swivel).

(B) minor circle circulation (green lines in Fig.1) is effected during drill string connections or other

tripping operations. In this case, the same complex design manifold directs mud flow via hydraulic

power arm to a dedicated sub screwed onto DP the latter being at that time off-loaded on rotor

slips.


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Further on, upon connection completion and special drill pipe torqueing, operator retracts the

hydraulic power arm away from the dedicated sub and the complex design manifold directs mudflow along the great circle. The sub with a back pressure valve system is run with every DP (or DP

stand) into bore hole.

In this way, mud circulation through borehole doesn't stop even for a minute, which fact essentially

mitigates the risk of wellbore integrity loss.

Fig. 4. Hydraulic power arm with a packer and dedicated DP sub


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Conclusion

PNG Drilling Company in cooperation with European manufacturers of drilling equipment has

developed efficient techniques of risk mitigation in oil and gas well drilling, the said techniques

being new for the Russian market.

PNG DC technologies ensure continuous mud circulation irrespective of operations' type as well as

managed pressure drilling achieved by means of in-process monitoring and regulation of

backpressure in wellbore while drilling through narrow drilling window zones.

PNG DC offers application of new technologies as an individual service at moderate day rates

comparable with top drive rental rates.

PNG DC technologies provide operators and contractors with additional toolkit for emergency

situation prevention in complicated oil and gas well construction.