Production Analysis Using Rate Transient Analysis

Abstract

Abstract Shale reservoirs have low permeability, high fluid efficiency, and low fluid leak-off making these types of reservoirs ideal for hydraulic fracturing. One of the biggest challenges in analyzing unconventional shale reservoirs is that their flow regimes stay in transient flow for a very long period of time. This aspect of unconventional shale reservoirs makes it very challenging to estimate recoverable resources along with reservoir properties such as fracture half length, permeability, drainage area, and fracture conductivity. Conventional decline curve analysis assumes constant flowing bottom-hole pressure, drainage area, permeability, skin, and existence of boundary dominated flow. Most of these assumptions are no longer valid in unconventional reservoirs. Therefore, it is crucial that not only rate, but also pressure and other reservoir parameters are taken into account to properly evaluate unconventional wells and determine the true flow capacity of their reservoir in linear transient flow. This study uses rate transient analysis (RTA) which plots pseudo normalized pressure versus material balance square root of time to estimate the productivity of Marcellus Shale wells. Our dataset is limited to a restricted area located in Greene and Washington Counties, Pennsylvania, with similar reservoir properties such as porosity, water saturation, pressure, and temperature. With limited variation in reservoir properties, the slope of the superposition plot used to calculate AK becomes a good metric for well productivity. The y-intercept from the same plot indicates the completions effectiveness of the well. The slope of the line for a well with zero completions damage intersects the origin. Any completions damage (skin damage) caused by poor completions designs or unfavorable reservoir properties will have a higher y-intercept in relation to the origin in the superposition plot. After performing this analysis on operated wells in the study area located in Washington and Greene Counties, the wells with the most successful completions methods were identified. This knowledge can then be applied for future wells in the same area for optimum production enhancements.