A Case Study of Massive Hydraulic Fracturing in An Ultra-deep Gas Well

Abstract

Proposal A case study of hydraulic fracturing has been performed in details in Jing-70 gas well located in north china oil field with the depth larger than 4000 meters.In the past, such kind of gas wells couldn't be fractured successfully as a result of early tip-screenout.Our study is on the base of past fracturing experience, and a lot of improvements have been made.The main character of our fracturing design is as following:core test of stress sensitivity is used in performance prediction model and determination of bottom flowing pressure;mini-frac is performed in order to get loss coefficient more precisely;large scale of proppant volume and high proppant concentration are used as principles;a new surfactant named DL-10 is developed to increase flowing back velosity;long term conductivity is inputted in to a new developed gas reservoir model so as to perform optimization more scientifically;multi-stage proppant pumping schedule is used so as to get an expected propped profile;pumping rate is requested to increase higher and higher under the limit of wellhead pressure according to three dimensional fracture propagation model;liquid nitrogen is used in the course of fracturing in order to enhance flowing back of fracturing fluid after shut-in;forced closure technique is utilized;systematic field quality control is used to ensure fracturing treatment to follow the design plan, and some modifications is allowed according to the change of treatment situation. After that, the well is hydraulically fractured successfully with 67 tons of proppant and sand to liquid ratio as high as 30%, which is the highest record in ultra-deep gas wells in north china. And post evaluation is performed completely including net pressure analysis. Overall, the fracturing design, treatment and post evaluation discussed in the paper for ultra-deep gas wells has a great significance in gas wells' stimulation and development as well. Introduction In north china exploration zones and caves, there are many ultra-deep gas wells which must be hydraulically fractured in order to evaluate reservoir characteristics more precisely. However, many hydraulic fracturing treatments in past have been failed, namely early tip-screenout because of some drawbacks in fracturing materials with relatively high damage, pumping parameters which are not fitted well with formation as well as the corresponding measures which are not adaptable. Therefore, an ultra-deep gas well named Jing-70 was selected as fracturing candidate to perform a new fracturing technology. Compared with former design and treatment in the same cave, there are totally 10 improvements just as mentioned above in the section of abstract.Fortunately, the fracturing treatment is very successful and the treatment level is very higher than ever before, which verifies that the method applied in the fracturing design and treatment is feasible and applicable.