MUD ANALYSIS AND CONTROL SYSTEM FOR DRILLING

Ziel

The project seeks to develop a comprehensive mud analysis and management system for use on the rig during drilling. For safe and efficient drilling, mud composition must be precisely controlled to achieve design specifications for density (for hole stability), rheology (for hole cleaning) and fluid loss (to avoid drill string sticking); and to minimise reactivity towards chemically active shales. The key innovatory idea in this proposal is to provide a new suite of measurements on the rig for real-time monitoring of mud composition during drilling. This capability is to be combined with new software tools describing mud circulation and interaction with the wellbore, downhole mud chemistry and mud conditioning to generate a set of new logs.
The effective use of ion analysis for cutting analysis has been illustrated by a Case Study in the Southern N. Sea. The technique for characterising the molecular weight distributions of oilfield polymers has been refined, and used to demonstrate the benefits of monitoring both polymer concentration and molecular weight for full control of drilling fluid properties.
The SCR chemical reaction simulator has been extended to include the kinetics of key reactions within a drilling fluid.
Experiments have been carried out to characterise further the osmotic swelling effects occurring in shale-mud systems, with increasing emphasis on small-scale work. In particular the effects of pore fluid chemistry and inert non-swelling silt material have been studied.
The effects of drainage on Pierre shale pore fluid water activity and the subsequent swelling sensitivity of the rock has been investigated in both small-scale experiments and the wellbore simulator. Drainage times are very long, leading to enhanced surface swelling sensitivity but also significant internal weakening of the rock.
An X-ray study of the influence of potassium ion exchange and water activity on the swelling of model shales has been carried out, to aid understanding of inhibitive potassium salt muds.
The project assessment concluded that the concept of a detailed Mud Analysis and Control System for use on a rig during drilling has been demonstrated to be technically feasible. Whilst cost of the system can be considerable, the potential benefits in terms of mud cost savings; and faster, safer, more reliable and higher quality drilling are sufficiently high to indicate that its commercial viability looks promising.
The project comprises four parts :
1. MUD ANALYSIS AND GENERATION OF A LOG
The development at SCR of an analytical method for ionic substances in mud filtrate is complete; this can be applied to mud solids and cuttings, allowing a complete characterisation of the mud. In the case of shales the cuttings cation exchange capacity (an indicator of clay type and hence reactivity) can be determined.
The development of analytical methods has now been extended to include polymeric and surfactant mud additives.
2. MODEL OF MUD CIRCULATION AND INTERACTIONS AND INTERPRETATION OF THE LOG
Time-varying data on the return mud cannot be used directly to derive information about downhole processes because of the distortion of signals produced by flow in the annulus. Four major effects need to be allowed for :
a) changes due to addition of drilled and eroded rock, influxes or deliberate additions of mud chemicals;
b) fluid loss;
c) chemical reactions between mud filtrate, mud solids and rock;
d) dispersion (mixing) caused by flow up the annulus.
To the extent that current physical understanding allows, software has been developed incorporating these processes; this forms a key component of an interpreted chemical log.
3. WELLBORE SIMULATOR EXPERIMENTAL PROGRAMME ON MUD/SHALE INTERACTIONS.
The SCR Wellbore Simulator has been deployed at intervals throughout the project to validate methods and models by direct experiment under controlled conditions. Three particular features of the Simulator deserve emphasis. First, muds are circulated in the Simulator at representative borehole pressures, temperatures and velocities through an annulus. Second, mud can be drawn off to provide laboratory samples for precision analysis. Third, shale rock samples of 60 cm diameter are used, so that considerable depths of penetration/erosion may be studied. The Simulator is equipped with ultrasonic instrumentation to allow changes in hole diameter through erosion or swelling to be measured continuously while circulating.
The large-scale Wellbore Simulator experiments have been supported by laboratory investigations of shale/mud reactivity in a high pressure diffusion cell. Its main purpose has been to provide data on the reaction between stressed, chemically active shales and mud fluids, especially on the role of cations in modifying the rate and extent of hydration swelling.
4. ASSESSMENT OF PROJECT
The final phase of the project has involved a full technical and economic evaluation of the results.

Programm/Programme

ENG-HYDROCARB 2C - Programme (EEC) of support for technological development in the hydrocarbons sector, 1986-1989

Thema/Themen

1.2 - DRILLING

Aufforderung zur Vorschlagseinreichung

Data not available

Finanzierungsplan

DEM - Demonstration contracts

Koordinator

SCHLUMBERGER CAMBRIDGE RESEARCH LTD

EU-Beitrag

Keine Daten

Adresse

HIGH CROSS MADINGLEY ROAD
CB3 0EL CAMBRIDGE
Vereinigtes Königreich

Gesamtkosten