John Yilin Wang

Study of borehole stability of Marcellus shale wells in longwall mining areas

With the widespread drilling of gas wells in Marcellus shale, there are high potentials for wellbore instability problems when wells are located in longwall mining areas, which in many areas such as southwest Pennsylvania, West Virginia, and eastern Ohio are being used for extraction of the coal seam overlaying the gas reserves. The ground deformation, caused by coal mining, could generate large horizontal displacement and complex stress change in subsurface rock. This in turn triggers ground movement which can cause casing failure, and thus interruption in the operation of the well that raises safety and environmental concerns. This could result in shutting down the well for repair, or permanent abandonment. Thus, it is critical to characterize the parameters related to the longwall mining process and to propose a general casing design guideline in such areas. In this paper, numerical modeling was utilized to simulate the complex ground conditions and resulting stresses and strains in longwall mining areas. A casing design spreadsheet was then constructed for design of appropriate selection of casings, based on the results of the numerical modeling. Our results were validated with field practices of wellbore design in southwest Pennsylvania. This paper also provides a methodology for investigating potential ground deformations, resulting stress/strain changes, and wellbore stability issues for oil and gas wells drilled in longwall mining areas in Marcellus shale or similar formations worldwide with active coal mining activities.

Well Completion for Effective Deliquification of Natural Gas Wells

Liquid loading has been a problem in natural gas wells for several decades. With gas fields becoming mature and gas production rates dropping below the critical rate, deliquification becomes more and more critical for continuous productivity and profitability of gas wells. Current methods for solving liquid loading in the wellbore include plunger lift, velocity string, surfactant, foam, well cycling, pumps, compression, swabbing, and gas lift. All these methods are to optimize the lifting of liquid up to surface, which increases the operating cost, onshore, and offshore. However, the near-wellbore liquid loading is critical but not well understood. Through numerical reservoir simulation studies, effect of liquid loading on gas productivity and recovery has been quantified in two aspects: backup pressure and near-wellbore liquid blocking by considering variable reservoir permeability, reservoir pressure, formation thickness, liquid production rate, and geology. Based on the new knowledge, we have developed well completion methods for effective deliquifications. These lead to better field operations and increased ultimate gas recovery.

Interpretation of Hydraulic Fracturing Pressure in Tight Gas Formations

The interpretation of hydraulic fracturing pressure was initiated by Nolte and Smith in the 1980s. An accurate interpretation of hydraulic fracturing pressures is critical to understand and improve the fracture treatment in tight gas formations. In this paper, accurate calculation of bottomhole treating pressure was achieved by incorporating hydrostatic pressure, fluid friction pressure, fracture fluid property changes along the wellbore, friction due to proppant, perforation friction, tortuosity, casing roughness, rock toughness, and thermal and pore pressure effects on in-situ stress. New methods were then developed for more accurate interpretation of the net pressure and fracture propagation. Our results were validated with field data from tight gas formations.

Feasibility of Waterflooding for a Carbonate Oil Field Through Whole-Field Simulation Studies

bbl of oil to date. It was noticedthat gas oil ratio had increased in certain parts and oil productiondeclined with time. This study was undertaken to better under-stand and optimize management and operation of this field. In thisbrief, we first reviewed the geology, petrophysical properties, andfield production history of PSU field. We then evaluated currentproduction histories with decline curve analysis, developed anumerical reservoir model through matching production andpressure data, then carried out parametric studies to investigatethe impact of injection rate, injection locations, and timing ofinjection, and finally developed optimized improved oil recovery(OIR) methods based on ultimate oil recovery and economics.This brief provides an addition to the list of carbonate fields avail-able in the petroleum literature and also improved understandingsof Smackover formation and similar analogous fields. By docu-menting key features of carbonated oil field performances, wehelp petroleum engineers, researchers, and students understandcarbonate reservoir performances. [DOI: 10.1115/1.4030401]