Accurate Estimation of Equivalent Circulating Density During High Pressure High Temperature (HPHT) Drilling Operations
- E. Ataga (Institute of Petroleum Studies, Uniport) | Joel Ogbonna (Institute of Petroleum Studies, Uniport) | Oriji Boniface (Institute of Petroleum Studies, Uniport)
- Document ID
- Society of Petroleum Engineers
- Nigeria Annual International Conference and Exhibition, 6-8 August, Lagos, Nigeria
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 1.11 Drilling Fluids and Materials, 1.7.5 Well Control, 1.6 Drilling Operations, 1.10 Drilling Equipment, 1.8 Formation Damage, 5.5.1 Simulator Development, 5.9.2 Geothermal Resources
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Error in equivalent circulating density estimation can be disastrous because of the narrow margin between pore and fracture pressure in HPHT wells. High temperature conditions cause the fluid in the wellbore to expand, while high pressure conditions in deep wells cause fluid compression. Failure to take these two opposing effects into account can lead to errors in the estimation of bottom-hole pressure on the magnitude of hundreds of psi.
This study involves the development of a simulator called HPHT-Density Simulator to simulate the wellbore(drillpipe and annulus) during circulation as well as the temperature and pressure profiles of a wellbore during circulation.
A Bingham plastic model was incorporated into a simulator called HPHT-density Simulator which was developed using Visual Basic to simulate the wellbore during circulation. The developed HPHT-density Simulator program interface is executed with a series of user forms,which will accept data pertaining to the wellbore, drilling fluid and formation parameters and return the temperature profiles in the wellbore and formation, pressure losses in the wellbore and ECD of the circulating fluid. The user can navigate between forms and input data at leisure using the "back?? and "next?? input bottons. Once values of all the necessary parameters have been entered into the program, the results are displayed on a "results?? forms.
The successful simulation of HPHT-Density Simulator shows a significant difference in the equivalent circulating density and bottom hole pressure profile for fluid circulation parameters of a Niger Delta well when the rheological properties were assumed to be constant as compared with when temperature-pressure varied. This can be adapted to drilling operations and thereby preventing downtime arising from kicks, blow-outs, lost circulation and formation damage due to wrong estimation of equivalent circulating density while drilling within narrow margin between pore and fracture pressure in HPHT wells.
A high pressure-high temperature (HPHT) well can be defined as one with undisturbed bottom hole temperature (BHT) at the prospective reservoir depth greater than 300oF(140oC) and either the maximum anticipated pore pressure exceeds 0.8psi/ft or pressure control equipment with a rated working pressure in excess of 10,00psi is required. It is readily observed that the conditions are harsher in such a well compared to the standard shallower well. A HPHT well is a critical well, where there are small design margins and where a well control problem is difficult to handle (Aadnøy, 1999).
Drilling fluids generally consist of a complex heterogeneous mixture of various types of base fluids and chemical additives that must remain stable over a range of temperature and pressure conditions. The properties of these complex mixtures, such as equivalent circulating density (ECD) and the rheological properties of the fluid mixture determine pressure losses in the system while drilling. It is often assumed that these properties and thus the equivalent circulating density (ECD) are constant throughout the duration of drilling activities.
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