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The Longwangmiao Formation of Cambrian system in the Moxi block of Anyue gas field is located at the paleo uplift of central Sichuan Basin, spanning Sichuan Province and Chongqing Municipality. With proven gas in place of 440.383 billion cubic meters, it is the largest monomer marine uncompartmentalized carbonate gas reservoir that has ever been discovered in China.

On September 9, 2012, formation testing at well Moxi-8 of Anyue Gas Field obtained a high-yield gas flow of over 1.9 million cubic meters, declaring the discovery of the Longwangmiao gas reservoir. On October 20, 2015, the Longwangmiao gas reservoir was put into production, with an annual capacity of 11 billion cubic meters provided by a 1bcm/a production test project, and the 4bcm/a and 6bcm/a production projects. By March 28, 2016, a total of 10.904 billion cubic meters of natural gas was produced.

The annual production capacity of 11bcm was achieved within less than three years since the discovery of the gas reservoir, registering a record period for an uncompartmentalized gas reservoir to be identified and put into production in China.

Longwangmiao gas reservoir is characterized by deep burial depth, high temperature and high pressure, poor physical properties and strong heterogeneity. How to identify pay zone, make fine lithologic description for more accurate reservoir evaluation, improve reservoir stimulation, and achieve fast drilling are the key issues for efficient exploration and discovery. Thanks to our new understanding on gas accumulation geology in paleo-marine carbonates and four innovative technologies for seismic reservoir prediction, fast drilling, logging evaluation and reservoir stimulation, rapid identification and efficient development of the gas reservoir have been realized.
Geological theories

  • A Late Sinian-Early Cambrian large inner-platform rift (Deyang-Anyue) was identified for the first time in the deep zone of Sichuan Basin, and gas resource extent in the Sinian and Cambrian systems of the basin was reevaluated.
  • The depositional modes of the Sinian Dengying Formation and the Cambrian Longwangmiao Formation were established.
  • Accumulation model of the cracking gas from the Sinian-Cambrian paleo-oil pools was established.
  • Two gas reservoir models, i.e. lithological-stratigraphic type of the Dengying Formation and structural-lithological type of the Longwangmiao Formation, were created in the structural setting of the giant Anyue gas field.
Applicable technologies

  • Technology series for deep zone seismic acquisition, processing and interpretation. Application of technologies including high-precision 3D digital seismic acquisition, pre-stack depth migration processing, carbonate karst fractured reservoir seismic description, and hydrocarbon detection, led to achievements in fine structural interpretation, paleo-structural evolution, reservoir and fracture prediction and hydrocarbon detection. Additionally, key parameters for large-scale structure maps, reservoir prediction and hydrocarbon detection were obtained, providing support for well location selection and OGIP calculation.
  • Seven logging evaluation models. Seven models include: pore structure evaluation, karst cave identification and evaluation, fluid property identification, pore effectiveness evaluation, quantitative parameter evaluation of heterogeneous reservoirs, fracture identification and effectiveness evaluation, and productivity prediction of complex carbonate reservoirs. Application of these technologies greatly improved the interpretation efficiency and accuracy.
  • Fast drilling. Optimized wellbore configuration, PDC bits, long-life screw drill, and high-quality drilling fluid enabled fast and efficient drilling in Gaoshiti - Moxi area.
  • Two proprietary technology series for reservoir stimulation. Considering large reservoir thickness, strong vertical heterogeneity, high temperature, high pressure, and deep burial depth of the Longwangmiao Formation, a compound stimulation technology has been developed which integrates deep penetrating acid fracturing, zonal acid fracturing and diversion acid fracturing, improving stimulation efficiency to 80%, and reducing the average formation testing cycle per layer from 30 days to 12 days. To address challenges caused by low permeability, low porosity, large spatial distribution, strong heterogeneity, high temperature and deep burial depth of the Dengying Formation, the reservoirs were stimulated by combining deep penetrating acid fracturing, high pressure acid fracturing and diversion acid fracturing, with a stimulation efficiency of 85%, and monolayer formation testing cycle decreased from 45 days to 21 days.
During the development of the reservoir, we creatively utilized a new technology to "foster high-yield wells", and deployed 30 target locations for high-yield wells in "two blocks and ten zones" that were considered most favorable for development. The number of drilled wells was greatly reduced by allocating horizontal or highly-deviated wells based on studies of the geography, landform, and reservoir thickness and spatial distribution, which enabled us to develop the gas field efficiently. By the end of 2015, the average daily gas output per single well during production test at Longwangmiao Formation exceeded 1.64 million cubic meters.

Gas identification and production were performed simultaneously, thanks to an innovative mode comprising integrated exploration and development, modular design, factory equipment manufacturing, skid-based construction and "PMT+EPC" for capacity building. Compared with traditional approaches, this mode not only reduced the land footprint by 20%, but also significantly shortened the construction period and the time to market.

Designed for "zero pollution and zero emissions", the development program employed the most proven technologies for the treatment of waste water and gas in an effort to build a green gas field up to the most demanding standards.

100% wastewater recycling

The produced wastewater goes into the biological treatment facilities through the collection system, and undergoes precision treatment such as aeration, air floatation, oxygen consumption, and anaerobic processing before moving to the further processing unit for electro-dialysis and evaporative crystallization. When soluble solid is crystallized and separated out, the treated water is qualified for recycling. The recycled water is either used for plant irrigation and worksite flushing, or supplied to the circulating water system for gas purification, thereby achieving zero discharge of wastewater.

99.8% sulfur recovery

The 4bcm/a Moxi Purification Plant has four sulfur recovery units, each with a designed capacity of 42 tons per day and equipped with CNPC’s proprietary CPS technology. In order to comply with the new national Environmental Protection Law, a renovation project of Shell Claus Off-gas Treatment (SCOT) for the 4bcm/a and the 6bcm/a units was implemented, increasing the total sulfur recovery rate to 99.8%, higher than the national standard of 99.6%.

  • The first giant gas reservoir of Cambrian system ever discovered in China.
  • The largest monomer marine uncompartmentalized carbonate gas reservoir in China.
  • New understanding on gas accumulation geology in paleo-marine carbonates, and innovative E&P technologies.
  • The record period of 37 months for a giant gas reservoir to be identified and put into production.
  • The first gas reservoir in China developed by drilling only highly-deviated wells or horizontal wells.
  • The average daily gas output per single well during production test exceeds 1.64 million cubic meters, the highest among sour gas reservoirs in China.
  • The sulfur recovery rate of purification plant reached 99.8%, the highest level in China.
  • The first gas purification plant in China that recycles 100% wastewater.
  • “Skid-mounted" mode is applied at all purification units and gas gathering & transmission stations.
  • All technical parameters of the gas wells, pipelines and purification units are integrated in the computer system of the production control center, setting an example of "Internet + gas production" for giant gas field development in China.