Rig-Site Monitoring of the Drilling Fluid Solids Content and Solids-Control Equipment Discharge
- J.M. Davison (Dowell) | Gerard Daccord (Dowell) | L.P. Prouvost (Dowell) | Alan Gilmour (Schlumberger Technical Services Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 1999
- Document Type
- Journal Paper
- 130 - 138
- 1999. Society of Petroleum Engineers
- 6.5.4 Naturally Occurring Radioactive Materials, 4.3.4 Scale, 4.1.5 Processing Equipment, 1.6 Drilling Operations, 4.1.2 Separation and Treating, 2.4.4 Screen Selection, 1.10 Drilling Equipment, 1.11.4 Solids Control, 1.11 Drilling Fluids and Materials, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties)
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Many of the key properties of a drilling fluid are adversely affected by the solids entrained during the drilling process. To control the impact of the drilled solids on the fluid properties the engineer at the rig site requires an effective monitoring tool. This paper describes the development and implementation of a technique based on X-ray fluorescence (XRF) spectrometry. The results are shown to be more accurate than traditional methods of analysis.
The speed and ease of use of the XRF technique facilitates multiple sampling from various points in the circulating system and effluent discharges. Two case histories are cited which demonstrate the use of the technique for monitoring the deployment of solids control equipment at the rig site and optimizing its configuration. The overall result is to improve well quality, control costs, and limit the environmental impact of the drilling process.
For any hole section to be drilled the chosen drilling fluid has specific properties to be maintained for efficient, cost-effective, drilling. The fluid density, viscosity, gel strengths, filter cake properties, inhibition levels, and lubricity are all adversely affected by the drilled solids entrained during the drilling process. As a consequence of the increased solids loading in the fluid the performance of the fluid deteriorates resulting in decreased rates of penetration (ROP), decreased hole-cleaning efficiencies, increased chance of differential sticking, and increasing the chance of solids plugging producing formations, therefore impairing future well productivity. In managing and controlling the solids content of the drilling fluid the engineer at the rig site requires an effective monitoring tool to allow frequent and accurate determination of the solids content in the circulating fluid and also effluent discharges from solids control equipment (SCE).
A technique has been developed which is being utilized at the rig site to overcome the limitations of the currently employed methods. The concept of measuring the solids in drilling fluids by X-ray fluorescence (XRF) was presented in 1993 (Ref. 1). This paper described the evaluation of this technique using a model calibrated with water based muds (WBM) comprised of barite, calcium carbonate to simulate drilled solids, and brines of various salts. The model used XRF spectra coupled with certain sample specific inputs to predict the concentrations of high gravity solids (HGS), i.e., barite, low gravity solids (LGS), water, and salt. Contamination experiments verified that substituting LGS phases of different chemical composition did not affect the predictive performance of the model. The quoted accuracy of the model was 0.32 volume percent (v/v%) for HGS and 0.8 v/v% for LGS. The resolution by which variations in LGS content could be detected was demonstrated to be approximately 0.3 v/v% absolute. It was estimated that the XRF technique was some ten times more precise than the traditional API retort technique for calculating solid volumes in drilling fluids.
It is the aim of this paper to document the developments brought to this technique during the last three years. The physical process of X-ray fluorescence and the use of a spectrometer at the well site are briefly discussed, along with the safety issues concerning the use of this technology. Coupled to the spectrometer is data-processing software with embedded standardization and quality control procedures. From the early WBM tests described above the functionalities of the software have been increased widely to include oil- and synthetic-based muds (OBM and SBM, respectively). Not only does the technique predict the solids and liquid phase concentrations for these muds, it also predicts certain ion concentrations. The development of this software, employing statistical modeling, is described with the prediction accuracies compared to the standard API techniques.
There are some 35 units operational at present. These are used in a variety of roles ranging from a well-site tool to a quality control technique for laboratory studies. Its prime role is that of a tool at the well site for frequent determination of the solids content of the drilling fluid, providing a tool for the engineer to monitor the solids fraction in the drilling fluid and proactively treat the mud. The speed and ease of use makes it particularly suited to the configuration and optimization of the solids control equipment. Two case histories provide examples of the type of information derived from this type of application.
X-Ray Fluorescence Spectrometry
The measurement is an emission spectroscopic technique which utilizes the physical principles of the interaction of ? or X rays with matter (Ref. 2). During analysis the sample is irradiated with a primary beam of ? or X rays for a fixed period of time. The energy is sufficient to interfere momentarily with the electrons surrounding the nuclei of the atoms in the sample and leads to three types of interaction:
Fluorescence is the most important interaction and occurs when a radiation particle (the incident photon) removes an electron from an inner energy shell of an atom. The vacancy created is filled by an electron from a higher energy shell which releases energy in the form of an X-ray photon. The photon energy is characteristic of a given element and the amount of photons is representative of the element concentration.
Scattering is a process where the incident photon interacts with the outer shells of elements and loses some of its energy. The energy remaining is dependent on the density of the sample and its chemical composition.
Absorption of a photon by the sample is a result of a complicated function of the chemical composition of the sample and generally decreases the number of photons available for fluorescence and scattering.
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