A New Ultra Inhibitive Ecological System for Offshore Drilling Applications

A New Ultra Inhibitive Ecological System for Offshore Drilling Applications

Aurelian Vasile Ganea , Avram Lazr , Marius Stan

The Petroleum Gas University of Ploiesti Romania

Abstract – Considering the on-going interest in developing and operating new productive perimeters at increasingly higher depths and temperatures, the enhancement in the rules required for the environment caused by removal of cuttings and limited performance of water based drilling fluids in hard to reach areas led to the need to develop high return drilling fluid systems and continuously improve them further based on data taken onsite.

The paper herewith envisages updating and bringing new data in view of elaborating a new drilling fluid of high performance and permanently adapted to well requirements.

Keywords: Drilling, Ultra-Inhibitive, Offshore

1. INTRODUCTION

   Technical challenges in drilling are new encountered in many of the hydrocarbon reservoirs worldwide. These challenges generally show up by drilling into narrow operating windows between pore-pressure and fracturing gradient occurring out of geological deposits or depletion of hydrocarbon strata inside the reservoir after a long period of time. The drilling narrow windows need strict control of drilling equivalent circulation density (ECD) or the use of such technologies that are able to handle the closest medium of borehole so that to allow for drilling progress by using other densities than prescribed in the density range, [2].

   The existing water based drilling fluids sometimes have limited performance compared to oil base muds or synthetic product based drilling fluids. Performances refer to:

   • Inhibition;

   • Rate of penetration;

   • Conditioning of drilling fluid;

   The ultra-inhibitive drilling fluid system with high properties of clay inhibition does not only improve drilling of upper sections but also has applications in the entire well drilling operation at high depths and temperatures,[1]. The ecologically improved drilling fluid stands for a plus in the technology of water based systems compared to the present applications of drilling fluid as they allow the ecologically improved drilling fluid system to be in comparison with oil and/or synthetic product based systems.

2. EXPERIMENTAL DESIGN AND TESTING

   The ecologically improved drilling fluid system is very inhibitive, elaborated and envisaged to assure a higher stability and capacity of drill-ability of reactive and dispersible clay formations. The proposed system may also significantly help cross with very good results the productive formations presenting maximum interest. The ecologically improved drilling fluid is designed to assure:

   • Maximum inhibition of clays;

   • Maximum stability of borehole;

   • An accumulation of displaced rock particles near to zero per the assembly of the drill string;

   • Easy maintenance of drilling fluid properties;

   • Flexibility in the density for work;

   • Flexibility in selection of the source of ions (potassium, sodium);

   • Applicability in various areas being sensible from point of view of environmental regulations.

     The main inhibitor of clays in the proposed ecologically improved drilling fluid is a polyamide followed by an cationic polymer acrylamide together with a poly-alkaline glycol assuring secondary inhibition of clays and stability of encapsulating cuttings, [4].

     Preparation of the ecologically improved drilling fluid is presented in the table 1

3. MEASUREMENT TECHNIQUES AND RESULTS The ecologically improved drilling fluid will allow for

being prepared by means of various brines and also with a large range in selection and utilization of densities. A laboratory study was carried out in order to monitor the manner how reactive solids incorporated within the proposed system affect the properties of the drilling fluid. A fluid having 1.56 SG/13.0 ppg density was prepared and tested (table 2). The fluid was contaminated as it can be seen below (Table 2) with 35, 70, 105, 135 and 235 kg/m3 of clay and MBT tests were conducted and tests on the concentration of the used inhibitors. No adjustment has been done as for depletion of clay inhibitors, [5]. [7].

Table 1. Preparation of the ecologically improved drilling fluid

Table 2. A fluid having 1.56 SG/13.0 ppg density was prepared and tested

16

70

60

50

40

3.5

3

2.5

2

30

MBT kg/m3

20 Inhibitor principal, % vol

10

0

0 35 70 105 135

1.5

1

0.5

0

235

Figure 1. Graphic represent the inhibitors variation function of proposed contamination

YP, lbs/100 ft2

After the first tests have been carried out, the ecologically improved drilling fluid system was subject to a second stage of tests, namely: analysis of the system rheology for a system having 1750 kg/m3/14.6 ppg at 500 C depending on various pressures applied, [6]

30

25

20

15

10

5

0

50

75

100

Temperatura , ºC

125

150

P=1 bar

P=136 bar

P=271 bar

P=408 bar

P=544 bar

P=680 bar

Figure 2. The dynamic shearing stress depends on pressure and temperature (fluid density:1750 kg/m3)

CONCLUSIONS

The following conclusions were drawn after the test has been performed:

• Measurement of the MBT value does not reflect the actual amount of solid reacting in the proposed system. Great part of reacting solids was absorbed by the main inhibitor and thus they act as inert in the MBT test. This is a significant indication of the inhibitive character of the fluid on the particle of clay within the mass of the ecologically improved drilling fluid system.

• Over 105 kg/m3 of reacting clay will be needed in order to deplete the concentration of the main inhibitor.

• The 1 secondary inhibitor is not significantly affected by the level of reacting clay. This is due to the fact this test is conducted in drilling fluid but also because the 1 secondary inhibitor is an

  encapsulating agent and its depletion only takes place at the cuttings surface.

• The effect of solids out of reacting clay on the system rheology is very low due to the high inhibition of the proposed and improved fluid.

• The system develops the concept of plane rheology, while gelations of the system show minor variation with temperature and pressure.

• The 2 secondary inhibitor is measured by means of a refractometer. This device has a low subtraction rate but significantly helps with encapsulating of rocks displaced together with an increase in the system lubricity thus reducing the friction coefficients.

• The results gotten herewith prove the stability of the system at high pressures and temperatures and also the fluid properties maintained even if facing high clay contaminations which makes the proof that the system proposed for analysis may easily frame the class of drilling fluids used in narrow window environments.

REFERENCES

1. Avram Lazr, Forajul Marin, Editura Universitatii Petrol Gaze din Ploiesti, 2005

2. Banciu,I. Aspecte privind reologia fluidelor de foraj,

   I.P.G. Ploiesti 1970

3. ***Advanced Project Engineering Program, Schlumberger, Houston, December 2011

4. ***Advanced Mud School, MISWACO, Houston, August 2011

5. ***Deep Water School, Houston, MISWACO, April 2008

6. ***Greater Ekofisk Well Control Course, CONOCO PHILLIPS / MAERSK Training AS Stavanger, January 2014

7. ***K&M , Hole conditions, Management & Monitoring Texas, 2009