Gas Well Production Decline Analysis

Arps categorized the rate decline of oil and gas well as exponential, hyperbolic and harmonic, and brought forward a technique of type-curve matching, which can determine the decline parameters and predict the further performances but cannot obtain the formation parameters. Basing on Arps rate decline law and combining the material balance equation with the pseudo steady-state deliverability equation, Fetkovich and Fraim et al established a suit of type-curve matching of gas-well (oil-well)rate decline, which can determine the formation parameters. At the same time, Fraim pointed out that, the rate is exponentially related to the normalized time for a gas well producing against constant bottom hole flowing pressure. On the foundation of this characteristic, limin set up a set of technique for automatically matching the gas-well rate decline with regression analysis.Founded on the research fruits of previous researchers, this dissertation is mainly concerned with the technique for automatically matching the gas-well rate decline of both normally pressured and abnormally pressured gas reservoir, and compares the calculated results with those of numerical simulation. The research content is following:(1)investigate the application confinement of the technique for automatically matching the rate decline of the normally pressured gas reservoir, that is, demonstrate the application confinement of this technique for various reservoir properties and different boundary shapes;(2)study the touchstone that justifies the formation parameters and the OGIP calculated through the technique of automatic matching;(3) research the effect of both pseudo-steady and whole production data on the calculated values; (4)establish the mathematical model for automatically matching the rate decline of abnormally pressured gas reservoir, for which the compressibility of both water and rock is beyond neglect; and that, determine the touchstone that confirms the calculated values.Grounding on limin's decline model and the new decline model presented in this paper, the module "rate decline" in the software "Analysis of gas-well load up and rate decline" is programmed.Through this module, the rate decline parameters, formation parameters and OGIP can be determined. This thesis has performed altogether 21 single-well numerical simulations , 37 automatic matching calculations and 1 field case analysis ; Comparing the results of numerical simulation with those of automatic matching presented in this paper, we acquire following conclusions:(1)For normally pressured gas reservoirs with extra low permeability, the decline parameters and OGIP calculated through limin's rate decline model greatly deviate their actual values.The boundary shape has little effect on the calculated results, to sum up, the calculated results forregular boundary shape with the well in center are better than other cases.(2)The normalized pressure is linearly related to the normalized time on the semi log curve, and also, the predicted gas rate can well match the actual gas rate, which is the touchstone for justifying the calculated formation parameters and OGIP. If the predicted gas rate can match the actual gas rate, whereas the back end of the semi log beeline bends upwards, this shows that the calculated OGIP is slightly larger.(3)The calculated results without consideration of unsteady production data are closer to actual case than those with consideration of all the production data.(4)For abnormally pressured gas reservoir, the model for automatically matching the rate decline, which takes the compressibility of both rock and water into account, can be used to analyze its rate decline. In addition, linear relationship between the normalized pressure and normalized time on the semi log curve, together with the good matching of actual gas rate with the predicted gas rate, is also the touchstone for justifying the calculated results, and the calculated results without consideration of unsteady production data are closer to actual case than those with consideration of all the production data.Through above investigation in this paper, the application confinement for limin's automatic matching technique and the touchstone for justifying the calculated results are presented; moreover, the thesis also advances a model for automatically matching the rate decline of the abnormally pressured gas reservoir.