The Bao 8 well block in Baode area is located in a complex surface zone within urban overlay areas

which imposes severe constraints on above-ground well placement. Furthermore

this well block is located in a subsurface region with complex tectonic structures

insufficient geological understanding

and significant variations in overall burial depth in the western part

which has long prevented its large-scale development. Since 2020

PetroChina Coalbed Methane Co.

Ltd. has initiated large-scale hydrocarbon exploration in the surface-subsurface dual complex area of the Bao 8 well block. The "Three Integrations" development model

i.e.

subsurface-surface integration

geology-engineering integration

and deployment-implementation integration

was adopted

and 100-million-cubic-meter level medium-shallow coalbed methane (CBM) platform was put in operation. Single-well investment was reduced by 7.8 %

and high-efficient development was achieved. Five key practical insights were summarized as follows:(1) In response to the complex subsurface geological conditions of the Bao 8 well block

a new round of fine structural interpretation and reservoir prediction was conducted based on comprehensively collected coal borehole data and field outcrop observations. A central sweet spot of 11.56 km

2

was selected as the key area for large-scale reservoir development and well deployment. (2) Guided by subsurface-surface integration and based on the updated refined structural and reservoir characterization results

differentiated well deployment was innovatively implemented in the sweet spot area. Following the principle of "horizontal wells in suitable geological formations

vertical wells in optimal reservoir zones"

a hybrid well pattern consisting of one large well pad with 55 wells (35 vertical/cluster wells and 20 horizontal wells) was deployed. Through this deployment

production from high-quality reserves of 5.43×10

8

m

3

and a pr

oduction capacity of 1.2×10

8

m

3

were achieved. (3) Under the guidance of the geology-engineering integration concept

horizontal well geosteering technology was optimized to ensure a high coal seam penetration rate of 98.6 %. Single bit-run drilling technology was applied to extend horizontal sections

with an average length of 1 006 m. Anti-collision control technology for dense well patterns on multi-well pads was adopted to ensure safe

efficient

and high-speed drilling in the Bao 8 well block. (4) To address the issues identified in previous-stage fracturing operations in the Baode area

an optimized moderate-scale fracturing technique was innovatively developed. Effective fracture volume is increased by this technique via high injection rate; fluid loss is reduced and fracture initiation efficiency is improved through application of 100-mesh sand in the pad fluid; effective propped fracture area is expanded with medium-size proppant; and fracturing costs are lowered by the use of low-cost simulated formation water. Under fluid volume control conditions

proppant volume was increased by 60 %

and the average sand ratio was doubled. (5) Through the integration of deployment and implementation

a large-platform

factory-style operation model was adopted

where simultaneous drilling was carried out by multiple rigs and zipper fracturing technology was applied

leading to a significant improvement in operational efficiency. At present

the total daily gas production of CBM wells in the Bao-8 well block has exceeded 26×10

4

m

3

. The average daily gas production per horizontal well is over 9×10

3

m

3

and that per vertical/cluster well is over 3×10

3

m

3

both of which exceed the design targets. The Bao 8 well block has demonstrated excellent gas production performance and has been recognized as a successfully developed medium-shallow CBM platform with 100-million-cubic-meter level production capacity in complex surface-subsurface areas

in China.