%0 Journal Article %T SELECTION OF OBM SALINITY THROUGH EFFECTIVE OSMOTIC PRESSURE EVALUATION IN CARBONERA SHALE FOR COLOMBIAN FOOTHILLS %A William-Armando Fern芍ndez-Vera %A Reinel Corzo %A N谷stor-Fernando Saavedra %J CT&F - Ciencia, Tecnolog赤a y Futuro %D 2010 %I Instituto Colombiano del Petr車leo (ICP) - ECOPETROL S.A. %X Wellbore instability in shales is attributed to many factors. Two of them are mechanical effects and physico-chemical effects. Drilling and drilling fluid cause physico-chemical interaction and the flux of water and ions that may alter the shale stress state through pore pressure and shale strength. This paper presents the analysis of the chemical osmosis phenomenon between drilling fluids and shale formations to evaluate the chemical parameters necessary for modeling the aqueous flux. These parameters are the drilling fluid activity (Adf), shale activity (Ash) and membrane efficiency (ME). This work also characterizes the shales for drilling purposes and describes an integrated methodology to obtain the magnitude of the chemical parameters. Furthermore, it is stated how the generation of effective osmotic pressure between the formation and drilling fluid define the water flux direction. Finally, the application of the results of the chemical analysis to Carbonera shale is presented. The design of laboratory tests for two mud formulations, Mud A and Mud B, and the field application is also showed. The Mud A is a balanced activity mud and the Mud B is a high salt concentration mud which may produce water flux out of the shale formation (dehydration) during drilling, in some sections of the wellbore, increasing the formation strength. The results presented in this paper will help to reduce the risks associated with wellbore instability during the drilling of shale formations and thereby lowering the overall non-productive time and reducing drilling costs. La inestabilidad de pozo en formaciones arcillosas es atribuida a muchos factores. Dos de estos factores son los efectos mec芍nicos y f赤sico-qu赤micos. La perforaci車n y el fluido de perforaci車n causan una interacci車n f赤sico-qu赤mica a trav谷s del flujo de agua e iones que pueden alterar la presi車n de poro, el estado de esfuerzos in-situ y la resistencia de la roca. Este art赤culo presenta el an芍lisis del fen車meno de 車smosis qu赤mica entre el fluido de perforaci車n y la formaci車n arcillosa para evaluar los par芍metros qu赤micos necesarios para modelar el flujo acuoso. Estos par芍metros son la actividad del fluido de perforaci車n (Adf), actividad de la formaci車n arcillosa (Ash) y la eficiencia de membrana (ME). Este trabajo tambi谷n caracteriza la formaci車n arcillosa para prop車sitos de perforaci車n y describe los m谷todos para obtener la magnitud de los par芍metros qu赤micos. As赤 mismo se establece como la generaci車n de una presi車n osm車tica efectiva entre la formaci車n y el fluido de perforaci車n define la direcci車n del flu %K fluidos de perforaci車n %K presi車n osm車tica %K osmosis qu赤mica %K shales %K estabilidad de pozo %K drilling fluids %K osmotic pressure %K chemical osmosis %K shales %K well stability %U http://www.scielo.org.co/scielo.php?script=sci_arttext&pid=S0122-53832010000100003