An Integrated Wellbore Stability and Sand Production Prediction Study for a Multi-Field Gas Development

Abstract

This paper presents a geomechanical study on the potential of wellbore instability and sand production for a multi-field gas development in offshore Peninsular Malaysia. The objectives of the study wereto develop strategies to maintain mechanical and time-dependent stabilities of extended reach wells, andto assess sand production risk in the development wells and eliminate unnecessary downhole sand control. The data required for the study include:in-situ stresses, including magnitude and orientation, and formation pressure,mechanical and petrophysical properties of the formations transected by the wellbore, andproperties of drilling fluid and its interaction with shale formations. The likelihood of wellbore instability and sand production for the development wells was assessed using in-house developed wellbore stability and sand production prediction tools. Mud weight stability profiles showing the variation of lower and upper bound mud weights with depth were developed for typical vertical wells. Critical mud weight contour plots which show the variation of lower and upper bound mud weights with wellbore azimuth and deviation angle for preventing mechanical wellbore instability were developed for various formations. In addition, a drilling fluid design methodology that can be used for quick and reliable determination of the optimum mud design (weight, type and chemistry) was developed for the fields. Critical drawdown and critical reservoir pressure profiles for assessing sand production potential in the fields were established. Sand production was found not to be a major problem in the early stage of production. However, depletion in reservoir pressure and water-cut can significantly increase sand production risk. Introduction The multi-field development consists of four gas fields located in Malay Basin, South China Sea (Figure 1). The fields with varying volumes of gas in place are to be developed as a group to optimize development cost and achieve economy of scale. The development plan includes extended reach wells, and there is considerable concern regarding wellbore stability in drilling the wells, its effect on drilling performance and the potential for this to severely impact both schedule and budget. Furthermore, the potential risk of sand production needs to be assessed prior to completing the wells. The production experience from the nearby fields has been mixed1. An integrated geomechanics study for the multi-fields was therefore conducted to assess wellbore stability and sand production potential in the fields. The data required for the study were obtained from laboratory and field measurements. The field data from five appraisal wells (study wells) were made available for this study. Mechanical properties of the reservoir sandstones and shales were established by conducting a number of unconfined compressive strength and triaxial tests on reservoir cores. The laboratory-measured mechanical properties were then correlated with the properties derived from openhole logs. The magnitudes of the in-situ stresses and formation pressure were derived from analysis of openhole logs, standard leak-off test data, coefficient of active earth pressure and qualitative stress information relating to the in-situ stress regime. The properties of drilling fluid-shale interactions were derived based on a database estabilished for a number of drilling fluids and shales encountered in the basin in previous studies. The likelihood of wellbore instability and sand production were assessed using in-house developed wellbore stability and sand production tools.

Formation Susceptibility to Wellbore Instability and Sand Production in the Hajdúszoboszló field, Pannonian Basin: Hungary

“…Geomechanical model for wellbore analysis is of utmost importance for a successful drilling program (Plumb et al, 2000) and field development plans. This geomechanical study is also important because of its adverse effects on drilling performance, and also it's potential to severely impact on both drilling schedule and budget (Wu et al, 2006). Due to the presence of overpressured formations in the Pannonian Basin, wellbore instability is often experienced.…”

Effect of Water Cut on Sand Production - An Experimental Study

“…Several experimental studies on the effect of water-cut on sand production have been reported on both loose sands and intact sandtones 4,[6][7][8]22 . The study presented by Skjearstein et al 6 and Wu et al 22 are laboratory sand production experimental studies that incorporated water-cut effect on intact sandstones.…”

“…The study presented by Skjearstein et al 6 and Wu et al 22 are laboratory sand production experimental studies that incorporated water-cut effect on intact sandstones. Bianco and Halleck 8 and Bruno et al 4 reported the results of water-cut effect for both oil and gas flow on loose sands.…”

“…The downhole sandstone samples were obtained from well preserved fresh cores 22 . Care was taken to avoid altering water saturation inside the sample during sample preparation.…”