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In the later stage of the oilfield development, Pulse Neutron Spectrum Logging is very useful to evaluate formation residual saturation, lithology and the water-flooded level of the reservoir in metal cased boreholes. PSSL pulsed neutron full-spectrum saturation logging tool is an integration of Carbon/Oxygen spectrum log, Gadolinium tracer spectrum log, neutron lifetime log and continuous activation logging. This tool may efficiently measure the residual oil saturation in the formation outside of the medium such as the casing and the cement sheath under the condition of different porosity and various of salinities. And these log methods may alternately be used so PSSL is capable of greatly improving measurement accuracy and the coincidence rate of interpretation.

Applications：

- Evaluate the residual oil saturation measurement under different porosity condition, quantitively analyze the porosity over 15%, semi-quantitively interpret the porosity of 15%-10%, qualitatively analyze the porosity less than 10%.

- Explore and evaluate those omitted oil-bearing layers and gas-bearing layers in abandoned wells and workover well.

- Measure and evaluate reservoirs and oil-water contact in the formation containing fresh water or water with lower salinity and unknown salinity where lithology is complex and mixed.

- In the water-drive reservoir project, evaluate oil saturation and fresh water migration of the formation in the oilfield.

- Using logging data, identify water layers and potential pay zones, evaluate the water-flooded level of pay zones and identify the water-flooded mechanism of the reservoir and find water bearing layers and provide evidences of controlling water and increasing oil production.

- Inspect cementing bond quality, check plugging effects and seek for bypass channels and omitted layers.

- Find coal layers and evaluate their levels.

Specifications

- Max. Pressure: 80Mpa    - Max. Temperature: 150℃/175℃，4h  

- Diameter: φ89mm/54mm   - Tool Length: 5.6m

- Neutron Yield: ≥1.5×108n/s  Operation Lifetime of Neutron Tube: ≥200h  Recommended Logging Speed: 50m/h

- Vibration: 29.4m/s2, 3-dimension, 0～55Hz, sweeping frequency for 3 times.

- Stability and linearity of energy gain within the whole temperature range: ≤0.5%。

- Measurement error: Neutron lifetime log: ±3% (in standard fresh water and salt water)

Spectrum logging: ±5% (in satruated water sand and saturated oil sand with the porosity of 35%).

Benefits and Features

- Obtain various formation parameters in a single logging run and improve the coincidence rate of interpretation.

- Adopt new type detector and spectrum data processing technique for widening the dynamic range, qualitatively determine the oil layer and water layer with porosity less than 10%, and quantatively interpret and evaluate with porosity over 15%.  

- The various parameters of the neutron generator are optimized and controlled to obtain a high neutron yield and a good yield stability and a long operation lifetime and improve measurement accuracy of PSSL.

- Turn the dynamic evaluation of each storage layer into reality by measuring activated oxygen, well temperature and natural gamma etc., figure out the water leakage layer, absorption layer and the stimulation measures.

- Equip completed spectrum processing and interpretation software, which makes the comprehensive evaluation and interpretation coincidence rate up to 80%, provide packaged solutions like local logging and post-logging measures.

Well logging example：

The following picture is 12.5 tons / day and 1.8 tons / day of oil production before XX well test in Jiangsu oilfield. According to our suggestion, plugging and shooting 6-10 layer; after measures, the liquid production is 3.5 square / day, and the oil production is 3.2 party / day. The results show that the production of oil from No. 16 low pressure layer is provided by level 6-10.

XXX well No. 113, 115 and 117 perforation production, before logging production of 2m /d, oil production 2m /d, water production rate of 1.7%. The interpretation results show that the main layer of the well is No. 117. The oil is the best in this layer, and there is a small amount of gas and dissolved gas in the layer. Because the layer belongs to the low energy layer, it causes the dissolved gas to overflow and exist near the well. The temperature of the layer is very low. The activated oxygen log shows that a small amount of water is formed in the layer and the neutron life is present. The upper part is gas bearing; the No. 115 layer is a differential oil layer. Activated oxygen shows that the reason for water formation is that after shut-in, residual production pressure difference can not drive the movement of oil, but still can drive the movement of water in formation. This phenomenon indicates that after the well is put into operation again, the water production rate may be higher, but it will soon drop to very low level, at this time the water produced is associated water.

The water site is 1564-1566 meters at the top of the 19 layer, and the activation oxygen shows more than 1562 meters of overflow and the lower flow of upper flow indicates that there is a micro flow in the 19-21 layer. It is presumed that the longitudinal fracture formed by the fracturing is the existence of the longitudinal micro seam. It is recommended to squeeze 1564-1566 meters to produce 1566.5 meters below the hole.

XXX heavy perforation 4173-4175m gas lift no output, shut in well. After filling and acidizing layer 5, 5 days after oil production, high water cut.

The explanation shows that the No. 5 layer belongs to the oil in the top of the thick layer, which is interpreted as low flooding, which indicates that the cones of the well water are reduced and the remaining oil reassembled; with the accumulation of remaining oil, the rise of the formation dissolved gas and the rise of the natural gamma show that the formation is used. Activated oxygen at 4183m-4187m is obviously abnormal, indicating the disturbance of water cone formed during production, which is the characteristic of oil-water interface pushed by bottom water.

The explanation shows that the No. 5 layer belongs to the oil in the top of the thick layer, which is interpreted as low flooding, which indicates that the cones of the well water are reduced and the remaining oil reassembled; with the accumulation of remaining oil, the rise of the formation dissolved gas and the rise of the natural gamma show that the formation is used. Activated oxygen at 4183m-4187m is obviously abnormal, indicating the disturbance of water cone formed during production, which is the characteristic of oil-water interface pushed by bottom water.

The oil well is interpreted as a dry layer (28) in well logging interpretation. This technique is used to test it. In the process of interpretation, it is found that the oil and gas response of the 28 layer and 2314 m -2316 meters has obvious oil and gas response, the perforated test production, and the natural gas production of 102 thousand M at present.