There are three main types of well production trends in the Bakken formation. Each decline curve characteristic of these production trends has an important meaning to the production trends of the Bakken Shale play especially type I and type II production trends. In the total of 146 well histories, there are 51 % of wells in Type I production trend. This high percentage of Type I production trend is showing the true characteristic of the Bakken Shale reservoir, which will be discussed later in this paper. Type I production trend has the reservoir pressure drops below bubble point pressure and gas releasing out of the solution. This can be seen on the GOR curve vs. time plot. The cause of reservoir drop below bubble point has been analyzed, and the production of oil in this behavior has driving force from the solution gas. In additional, two linear flow regimes have been observed by looking at the log-log plot of rate against time plot of type I well. In a type II production trend, production is primary from the matrix. Reservoir pressure is higher than the bubble point pressure during the producing time and oil flows as a single phase throughout the production period of the well. GOR curve is almost constant during the production period. A single linear flow behavior is observed in Bakken Shale play of type II wells. This behavior is characterized by a half-slope on the log-log plot of the oil rate versus time plot. A type III production trend typically has scattering production data from wells with a different type of trends. It is difficult to study this type of behavior because of scattering data and it will lead to uncorrected interpretation for the analysis. Calculation procedures are given for OIIP estimation, and the area of matrix drainage between fractures, Acm.

Pressure transient analysis (PTA) is typically performed on pressure BU data acquired over a period from a few hours to a few days, while production data analysis (PDA) is performed with production data acquired over a period of a few days to several years. Recent approaches to extending a pressure BU response by deconvolving production data seem promising, but simple rate-normalized pressure (RNP) and its derivative may be more straightforward provided redundant data and artifacts are eliminated in the RNP processing. This paper offers a unified PTA-PDA analysis combining pressure BU deconvolution with the RNP. Using the RNP as the indicator of the late-time behavior, the unified PTA-PDA analysis can provide a virtual constant rate drawdown response for the duration of the production data including the early time response from a selected pressure BU transient. The virtual pressure change and, in particular, its derivative provide trends easily identified as flow regimes suggesting model features that must be included in a simulated drawdown intended to match the unified response. A model match with the virtual drawdown resulting from the unified PTA-PDA analysis offers a model consistent with the entire production history that can be used to forecast future production behavior and reserves for the well. Synthetic and field examples illustrate the approach.