Abstract

The measurement of Annular Pressure-While-Drilling (APWD) is widely used as a vital tool today; however, measurement of pressure while running the casing or liner is not available. This paper presents field data demonstrating the use of a real-time, downhole pressure modelling software to provide vital downhole hydraulics. This software was used recently on two critical North Sea wells to ensure that drilling and running of casing and liner could be done within safe margins under a narrow fracture/pore-pressure condition. The description of the hardware set-up and real-time parameters used and its communication with the central, data-logging computer are also included.

In order to verify the accuracy of the software, the computed pressure data was compared with that measured by APWD while tripping in and out of both wells. The measured data during tripping was recovered from the tool memory after the trip. Results demonstrated the close correlation between the calculated and measured data that was observed prior to running casing/liner. This gave the rig crew confidence to rely on the hydraulics information given by the software when running the liner. The software was then used to guide the casing crew to run the liner successfully.

Introduction

Many hydraulics software programs are available today for use in well planning and in daily drilling operations to model downhole pressures and equivalent circulating densities (ECD). However, all these software packages require manual data input of real-time variables to simulate real operations.1–4 The real-time hydraulics software5 reported in this paper has been developed and now successfully used on 50 wells in the North Sea, Gulf of Mexico, South/Central America, and offshore West Africa. This software receives real-time data on drilling/tripping parameters from the mud logger (or central data provider) and sends computed data back for display using the rig data network. Separate displays for wellsite, or off-site displays for office personnel via a remote data link have also been used. The software was developed to assist downhole dynamic pressure management in drilling deepwater, HTHP and narrow pore/fracture pressure margin wells. In most applications where the software was utilized, annular pressure-while-drilling (APWD) measurements were also used to provide a "what is" vs. a "what should be" comparison that has been useful for making critical decisions.

The real-time software was developed following the successful application of a conventional hydraulics program which is based on two evolutionary engineering concepts to significantly improve the understanding and application of drilling fluid rheology and hydraulics under field conditions. The first concept subdivides the well into short increments and considers the effects of variable downhole rheology and localized well parameters. This permits 4th-dimension analysis (versus time) of rheology and hydraulics. The second concept takes full advantage of available rheological data (field and laboratory) for the specific mud in use. Data are combined into unique "data cubes" which provide shear-stress values for different combinations of shear rate, temperature, and pressure.

More accurate predictions are now possible for downhole mud rheology, fluid density, pressure losses, hole cleaning, and surge/swab pressures while tripping. Achievable benefits include:

  • reduced incidence of lost circulation,

  • improved drilling performance,

  • fewer drilling problems, and

  • better information for effective decision-making.

Catalysts for this advanced technology, which targets oil- and synthetic-based systems, are the recent availability of high-quality field measurements, inexpensive computer power, and positive changes in several oilfield paradigms.

Software Description

This paper presents the application of two hydraulics software packages:

  • a standard hydraulics program with manual data input; and (

  • a real-time hydraulics software system with automated data input of critical variables. Focus will be on the latter.

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