HYDROCARBON PRODUCTION DURING UNDERBALANCED DRILLING -A MATHEMATICAL MODEL TO PREDICT WELL PRODUCTIVITY

摘要

When a well is drilled underbalanced, formation fluids flow into the wellbore from any permeable formation in the open-hole section. It is possible to use the volumes of produced hydrocarbons, from a well drilled underbalanced, to provide an indication of the productivity of pay zones that have been penetrated (GRI, 1997). In calculating the productivity of wells, the common assumption is that inflow into the well is directly proportional to the pressure differential between the reservoir and the wellbore as well as the increase of well bore length (as the drilling proceeds the length of the well bore increases). The increase in the producing length provides a unique transient effect that can be used to analyze reservoir performance and to estimate certain reservoir parameters such as reservoir thickness, permeability, and the trend of increasing or decreasing productivity along the wellbore. As formation being drilled underbalanced, it is possible to produce hydrocarbons from permeable zones, therefore earlier benefit could be acquired by company as producing phase began. The advantage of underbalanced drilling is predicted by compare production wells data that drilled overbalanced with skin and if skin not included in field "X". Underbalanced drilling can improve production rate because no skin occur. This paper presents a mathematical model to predict the total hydrocarbons gained during underbalanced drilling. Vogel equation is used to calculate the influx while drilling reservoir section. Multiphase flow analysis will be discussed also as its effect to bottom-hole pressure calculation. KUnderbalanced Drilling;;Well Productivity;;Mathematical Model