Majeed, Arshad (Oil and Gas Development Company Ltd. Islamabad) | Jadoon, Mohammad Saeed Khan (Oil and Gas Development Company Ltd. Islamabad) | Jahangir, Saleem (Oil and Gas Development Company Ltd. Islamabad) | Andrabi, Aftab Hussain (Oil and Gas Development Company Ltd. Islamabad) | Ahmed, Bashir (Oil and Gas Development Company Ltd. Islamabad)
Integrity of well structure is a vital factor to produce hydrocarbons fromsubsurface. It is important that well structure along with cement behind thecasings remains intact to get controlled and risk free production during lifeof a well. This objective is achieved by making every effort to ensure goodcement behind pipe and selecting suitable well tubulars honoring reservoirfluid composition and fluid flow rates. In case the criteria of well integrityis not met, flow of fluids behind casing and communication between tubularscreate problems and may lead to uncontrolled flow of well fluid creatingenvironmental and safety hazards.
Bagla gas field is located within the Indus Basin with producing horizon inLower Goru Formation of Cretaceous age. This is a single well field, which wasdrilled by Phillips Petroleum Exploration Ltd during 1988. Later on OGDCLacquired this field. The field could not be developed due to its marginalreserves, remote location, non-availability of gas buyer in near vicinity ofthe field and non-attractive economics in case gas is sold to SSGCL due to highcost of pipeline quality gas to SSGCL gas transmission network.
During April 2004 gas channeling to surface was observed in the nearby arealocated within a radius of 2-3 km from the Bagla well. This gas channeling wascausing environmental and safety hazards in the area. This paper discusses themeasures taken by OGDCL to diagnose the cause of problem and efforts made tocontrol the well to contain the environmental and safety hazards in thearea.
Bagla is a single well gas condensate field located in Thatta ExplorationLease. The field is located about 150 km East of Karachi and 87 km South ofHyderabad. Nearest OGDCL well Nur # 01 is located at 3.5 km towardssouthwest.
Numerous investigators have studied the various factors that influence the ultimate strength of model mine pillars, such as ratio of height-to-least width; restraint or friction on the top and bottom; 1, 2 the effect of stress distribution in pillars on their strength; 3 and the scaling factors involved in applying the results of model pillars to full-scale pillars. However, the load-bearing capacity of pillars after initial failure does not appear to have been investigated. Yet many mines employ methods in which small pillars 4 or pillar remnants are left systematically; these pillars crush as mining progresses and, of necessity, affect the behavior of surrounding rock even after initial failure. The effect of such crushed or crushing pillars depends largely on their load-deformation characteristics.
This chapter presents the results of a preliminary investigation to determine the load-deformation characteristics of a few model mine pillars to and beyond initial failure.
Various investigators have also studied the elastic and viscoelastic behavior of mine structures. In such studies, computers are frequently employed to obtain numerical results by the finite difference or finite element methods. It would be entirely feasible to write a program that would approximate the load-deformation characteristics of pillars to and beyond the crushing stage if these characteristics were known. More accurate information on the induced stresses and deformations in overlying strata and on surface subsidence could be obtained, information which should result in better strata control by enabling the engineer to calculate more accurately the effects of changes in pillar spacing, size, and shape.
The model pillars were all made of Indiana limestone having a uniaxial compressive strength of approximately 7000 psi. All pillars were 1-J in. high and had a volume of 5 cu in. but had different shapes, as shown in Fig. 1. The tops and bottoms of specimens were ground fiat and parallel on a surface grinder. Models were then cut into the different shapes with a diamond saw and no attempt was made to further finish or smooth the sides.
A Tinius Olsen hydraulic testing machine and an Olsen electronic recorder were used for conducting the tests. The testing machine had a swivel head but, after ensuring that it was parallel to the top of the test model, it was wedged to prevent further movement. The loading table was set to travel at a constant rate and the recorder plotted table movement, i.e., yield of the specimen, in inches vs. applied load. On the graphs (Figs. 2-7), however, the yield is shown as a percentage of the initial height of the specimen rather than in inches. The yield of the Tinius Olsen machine without a specimen was measured and at 80,000 lb was found to be equivalent to about ½ % yield in a specimen, with half of this yield occurring within the first 1000 lb of load. This was negligible compared to the overall yield in the specimens, so no correction was made in the graphs except for adjusting the origin of the graphs to pass through a common point.