Interwell tracing by environmental isotopes at Fimkassar Oilfield, Pakistan.

Water flooding is an important operation to enhance oil recovery. Movement of injected water is traced to test the performance of the water flood and verify suspected geological barriers or flow channels, etc. This paper describes the application of environmental isotopes as interwell tracers at Fimkassar Oilfield in Chakwal District, Pakistan. Water flooding was started in March 1996 in the Sakessar formation (Eocene). When water appeared in the production well in June 1998, isotopes (18O, 2H and 3H) were used to determine the breakthrough/transit time of the water flood and the contribution of fresh injected water. Water samples were collected during June 1998-August 1999 from the injection well, the production well, and some other fields for reference indices of the Sakessar formation and analyzed for the 18O, 2H and 3H, and chloride contents. The isotopic results confirmed the breakthrough of injected water and indicated that the water in the production well was a mixture of the injected water and the formation water. The initial breakthrough time was 27 months. The contribution of injected water varied from 67% to 80%. This percentage did not change significantly from the time of breakthrough until the last sampling indicating good mixing in the reservoir and the absence of any high permeability channel. Chloride content did not give any information about the hydraulic connection between the injection well and the production well. The study proved the potential of environmental isotopes for interwell tracing.

Origin and subsurface history of geothermal water of Murtazabad area, Pakistan--an isotopic evidence.

The Murtazabad area represents one of the major geothermal fields in Pakistan, with seven hot springs lying along the Main Karakoram Thrust. Discharge of the springs is 50-1200 l per minute with the surface temperature from 40 to 94 degrees C. Environmental isotopes and chemical concentrations have been used to investigate the origin and subsurface history of thermal water. Four sets of water samples were collected and analyzed for various isotopes including 18O, 2H and 3H of water; 34S and 18O of dissolved sulphates and chemical contents. Isotopic and chemical data show that the origin of thermal water is meteoric water. On the delta-diagram, delta18O and delta2H data plotting below the local meteoric water line with a slope around 12.3 show that the original thermal water receives recharge from precipitation at higher altitude (3000 m) and undergoes delta18O shift of about 1 per thousand due to exchange with rocks. Different correlations between isotopes, temperature and Cl indicate that the observed isotopic compositions have evolved due to mixing of different proportions of shallow water at different spring paths during movement of thermal water towards the surface. It is also inferred from the tritium data along with delta18O and delta2H that the circulation time is long and is estimated to be more than 50 years.

Fat absorption in persistent diarrhoea using 13C-labelled trioctanoin breath test.

A study was undertaken to investigate intestinal fat absorption in young children suffering from persistent diarrhoea in comparison with normal children of similar age. Absorption studies were performed using the breath test technique. Following oral administration of labelled triglyceride ([13C]trioctanoin), interval breath sampling was done for 6 h. The time course of excretion of 13CO2 in the breath was determined by isotope ratio mass spectrometric analysis of the gas samples. Excretion curves were constructed from the mean values of 13CO2 dose (per cent) excreted at each time point in breath samples and areas under the curve were determined for diarrhoea cases as well as for normal subjects. The time course of 13CO2 excretions and areas under the curve thus obtained were compared with each other and also with a reference study in which data from known malabsorption cases were available. The time of peak 13CO2 excretion in diarrhoea cases ranged from 60 to 240 min (average 150 min) compared with 120 to 270 min (average 195 min) for normal subjects, the level of peak of 13CO2 excreted/h was 4.8 +/- 1.2 per cent in diarrhoea cases and 5.3 +/- 2.3 per cent in normal children (NS). Mean areas under the curve for the two groups were 18.9 +/- 3.4 per cent for normal and 17.6 +/- 4.1 per cent dose 13CO2 excreted/6 h for diarrhoea cases (NS). These results indicate that intestinal absorption of medium chain triglycerides was not impaired significantly in the cases of persistent diarrhoea studied.