Reservoirs of Shu-one area of Liaohe oilfield Company of Petro China reserves extra heavy oil. The reservoirs are characterized in high porosity, high permeability, thick pay, bedded formation, relatively shallow burial, low original reservoir pressure and pressure and bad physical properties of crude oil. CSS is implemented in production. Casing failure often occurs due to short production time in a cycle, frequent steam injection and sanding-out of formation after several cycles of huff & puff. Mechanism studies in casing failure presented in this paper shows that the frequent variation of thermal stress as well as non-uniform loading over the perforation intervals due to sanding-out are major causes for casing failure.
Casing with thicker wall and higher steel grade is used in well completion along with thermal stress compensator, prestressed casing and end locker. This increases casing collapse resistance capacity and resists casing failure due to nonuniform loading due to sanding-out. Casing life is extended significantly due to reduced casing failure through the use of advanced well completion technologies, resulting in improvement of development efficiency of the extra heavy oil.
Reservoirs in the Shu 1 area of Liaohe Oil Field of China are abundant in extra heavy oil resources with OOIP in amount of greater than 100 millions tonns. He reservoirs are characterized in high porosity (about 25%), high permeability (about 1.0 µm2) and relatively thick pay (40 ∼90m). The major recovery technology is Huff & Puff. The current production capacity is over 2 millions of tonns annually.
The development of extra heavy oil resources in the Shu 1 area started in 1996. Well completion techniques have been continuously improved in order to fit for Huff & Puff production scheme of the extra heavy oil.
In the early development stage from 1996 to 1999, N80 casing was adopted as production casing and P110 casing was used in the perforation interval as a measure to prevent from deformation. The results were not satisfying with the application, the average casing deformation occurrence was at the 3.5th cycles and 80% of the wells were deformed. A detailed study and experimental test were carried out from 1999 to 2000 and a non-API specification casing of steel grade TP100H was developed. The performance of all major parameters was improved significantly (Table 1). It can be seen from Table 1 that the average number of cycles before casing deformation extends to 5.1, the percent of casing deformation declined to 47.8% and maintained no change until 8 cycles. although the casing deformation was under control, it can't satisfy the requirement of oil field development. An effective way to extend casing's life should be found.
According to the statistical data analysis, casing deformation in the extra heavy oil wells is characterized as following:
Casing deformation frequently occurred in the 3rd to 7th cycle.
Based on the statistical data from 493 wells with casing deformation problems, it is found that the casing deformed for 344 wells occurred from the 3rd to 7th cycle, accounting for 70% of the total casing-deformed wells (Fig. 1).
